I just want to minimize dishes taken to a BBQ--marinating pork chops in a lemon/herb/olive-oil baste along with some chicken skewers. Is there anything to worry about with trichonosis when preparing pork in same dish with other meats at room temperature? I can't imagine it's a problem, but you never know...
Don't worry about the pork contaminating the chicken, but rather vice versa. A good rule of thumb with chicken is to treat it as a biohazardius contaminant. Because it is. Salmonella is present IN chicken meat, unlike other meats where you will only find microbes on the surface. Your marinade doesn't seem particularly inhospitable to pathogen growth, so cross contamination would be a nontrivial concern. OK, if you overcook your pork chops as some insist on doing, it shouldn't be much of a concern. However, may as well be safe and split the marinade between two ziploc bags. It's a small effort to mitigate risk.
I wouldn't worry about trichinosis. In the years 1997-2001 there were 21 pork related incidents in the entire US - so only 5-6 cases a year.
I spent a few minutes Googling this and it seems like most of the posts I read that advised against it were more "better safe than sorry" type responses than anything grounded with experimental data. Furthermore, your specific marinade has lemon juice, which will make it harder for bacteria to grow.
I personally think you're safe...but I do want you to reconsider what you're bringing. If you're going to BBQ chicken and pork marinated in exactly the same thing, won't they taste pretty much the same? It doesn't seem worth it to even get the second type of meat for the flavor/variety payoffs. It'd be like buying BBQ Lays and BBQ Pringles together.