If their little bio on the lecture poster misidentifies them as registered, that's a potential problem.  If not, anyone is allowed to talk about anything, strictly speaking.  Lots of designers give ponderous, often meaningless lectures about "architecture."  We may resist, heckle, or complain.  But it happens all the time.

Did the person claim to have certain academic degrees or a professional license when they, in fact, did not?  That would be grounds to rescind the invitation and cancel the lecture.   

A lot of unlicensed people without formal training work in design fields and don't fraudulently claim false credentials, but they don't go out of their way to admit their status either.   Do they know their stuff?  Sometimes.  It sounds like the big firm that employs this person thinks so.

Whatever the case is, whoever introduces the speaker should mention the persons academic background, or lack thereof, at the beginning of the lecture.  

It's ironic that an apparently successful practitioner with no academic design training is speaking at a prestigious and expensive university design school.

from what I can see, this person has design degrees from outside the US, is that your issue?

foreign design degrees are great. Actually this person doesn’t have any professional design degrees

So the question is really whether that’s something to be concerned about as a group of professionals, or not?

When does it become Fyre Festival-esque?

I see no issues. Maybe the students will learn something practical about the working world. 

So, no degrees or certifications.  Here's a more relevant question: Does this person know anything about landscape architecture?

They should have gotten Kanye West.

It's just a freakin' lecture. It is like presenting work your employees produce., as long as the lecture is interesting :) One of the principals of a landscape architecture firm here in town is actually a philosopher...no design background at all. Do managers need to know what the people do they're managing? Might be refreshing to listen to a lecture about (landscape) architecture without all the archispeak. 

I would say you should be prepared to back your claims in court if this person,(it's not hard to find who it is) finds this posts and decides to sue you for libel. 

As rando says, it's just a lecture, anybody can speak of what they know, but you can't go around badmouthing someone just because you have a personal problem with it.

Last, do you think this "Large Design Firm" would hire and make associate of someone who's not qualified to do the job or to represent them?

Kind of like Ando, FLW, or Pawson giving a lecture on architecture. The nerve! I am sure there is nothing to be learned there. Shoot the poser!

This person does have three degrees related to landscape and design, and about 8 years of related experience.  You seem uncomfortable with the lack of an LAAB or NAAB accredited degree or something equivalent.  I'd keep in mind that they are experienced in the field, they lead the landscape department at a widely respected firm, they aren't claiming any particular license or certification, and the state in which they work doesn't even require an accredited degree for licensing, nor do most US states - and this person doesn't appear to be using any regulated terms in describing their work or their position in that firm.

If you feel strongly that guest lecturers should have accredited professional degrees I suppose you could voice that to the university department's lecture committee.  Obviously you can also choose not to attend the lecture.

Personally I don't see it as problematic - it's a person lecturing about their experience, in a field in which they do in fact have experience and education.  Getting too hung up on accreditations and titles will drive you crazy as you get into your career - you'll encounter many, many people who didn't get to their positions via accredited professional degree programs.  Many are nonetheless experts in their fields.

"Has anyone encountered what seems to be false representation of professional disciplines?"

Yes, Alexandria Ocasio-Cortez as a member of Congress.

Money says the lecture isn't about Landscape Architecture but about Landscape as it relates to ARCHITECTURE.

The lecture is about "Understanding the Benefits and Challenges of Integrated Multidisciplinarity".  That probably means it's about the lecturer's experiences as a landscape designer working with architects and other disciplines.  The speaker is the head of landscape design  in a large design firm, and has worked in that capacity on a good long list of projects.  I don't really get the OP's objection - how is it deceptive and misrepresentation for someone to speak about their professional experience?  The accreditation of the speaker's foreign degrees seems entirely irrelevant, unless maybe they were lecturing on "how to get into an accredited professional degree program" or something like that.  I'd vote for just skipping the lecture if you're offended by the lecturer's lack of a certain degree.

Given the lack of required experience, this person does not qualify, and
will never qualify as a professional practitioner in any design field.

Huh?  They're the head of landscape design... but you think they have a "lack of required experience"?  If this person wants to become a licensed landscape architect I'm sure they would satisfy the experience requirements, and a professional degree isn't a requirement - you can get that license by several different experience+education tracks.  

its not a problem, there is no misrepresentation, probably going to be a good lecture, you should go and listen and see for yourself.

hospitals are run by people who are not doctors. This is not even close to that kind of gap, so why the worry?

It's become clearer as the thread's gone on that the OP's objections stem from experience working with this lecturer on a project once.  It's possible that the lecturer is incompetent, despite a strong resume that suggests otherwise.  That happens.  Most of us can think of cases we've encountered in our professional lives.  I can sort of understand the resentment and concern that would result from seeing a bumbling consultant land on the academic lecture circuit - but I don't think it will ever be practical to ban people from the lecture circuit based on that sort of anecdotal objection. 

The far more ridiculous part of the OP's argument is claiming that the lecturer has no experience, no related education, the firm doesn't do landscape architecture, etc.  The firm has won numerous landscape architecture awards all over the world and employs many landscape architects who have stamped a mountain of landscape plans that are on file with AHJs, including right here in New York and other US states. Collectively they've got the credentials to practice pretty much anywhere.  The lecturer in question has extensive related education and has held past positions in landscape design. 

... and the lecture already happened so it's all moot.

i get totally get your point... but i do think forming an opinion of a lecture/lecturer base on their titles or lack thereof before you've heard them speak is a problem. personally, i've grown tired of the idea that having more degrees, titles, awards etc makes you appear more knowledgeable or more of an expert.

i've heard many people speak who were just as or more interesting an insightful and they had jack shit on their resume.