I would recommend a power vent hood, if it is a solid roof, you will want something to remove the smell and smoke form the area underneath.

"I hate doing these, and have always deterred clients from putting grills under overhead construction, but this particular client wants a grill [...] I am very paranoid about all issues fire related [...] typically I refuse to do grills within 10 feet of the residence, but there are no options on this project, and the client is a big time foodie who wants a nice grill station."

Is the pay that good? 

I'm only halfway joking with that; there are some legitimate questions here you probably need to ask yourself. If a client is asking you to design something you don't feel comfortable with, are they compensating you enough to take that risk? Is there a level of compensation that would make you feel comfortable doing it? Are they providing a waiver of liability, or something else, that might make you feel better? Would you feel better hiring someone with experience doing this as a consultant and letting them handle it? Would you and the client be better off parting ways and letting someone else handle it? How big of a deal is it to you?

I always insist that the kitchen be outside in the middle of a field on an island surrounded by at least a quarter mile of open water.

If you are not comfortable with it, irrespective of the money involved, walk away from it. After they haul the kids to the hospital with severe burns does it really matter who has liability?

Everyday Architect, it is a small part of a much larger project that I am very excited about.  The client is giving me much creative freedom with the rest of the project, and I feel that it will be a major portfolio piece when done.  His only real "must have" is this covered grilling area.  The attached patio cover will be of non-combustable construction and will have a range hood that meets the manufacturers requirements.  I am just very cautious with these grills because there are variables like grease fires and such that are probably not factored into the manufacturers clearences.  Just looking for some reassurance that I am not missing anything.  I will ask the local fire marshall and code officials for their take as well.  

I'm not sure how much reassurance you'll be able to take from some anonymous people on an internet forum with no skin in the game. 

It sounds like your seeking reassurance from actual officials that you are doing things correctly. I'd recommend continuing down that path. Have you also asked the manufacturers about the variables you're concerned about? If you're still uncomfortable after all this, would you really overlook your gut feeling because the larger project is exciting and you think it will be a portfolio piece? WWFLWD?

louis80- 

I am glad to hear it will have a range hood to remove smoke and smelll. Enough crap in a gas grill- grease, unburned wood chunks, asparagus that fell through the grates, etc... can cause one hell of a repeating smoky grill-fire situation, that while not necessarily an imminent safety threat, will wreak havoc on the outdoor kitchen enclosure finishes until someone cleans the grill. 

I would strongly consider a design that allows for easy cleaning of the grill to encourage this sort of upkeep, especially if this will be a well used feature.