Do I need to worry about marinade dripping in a gas grill?
Yah aluminum foil is considered a bad thing on grills, from what I have heard.

They sell grill grates for such things if you like, me, I just turn the flame on the grill down a touch and deal with the occasional flame-ups. They actually do no harm. And if you have a grill brush to apply the marinade while cooking with a l o n g handle (what I use) you can keep your hands farther away from the (potential) flame.

Anyway a little bit of char from the flame is a good thing and adds flavor to the meat!