If you want more bark - do not foil. While foiling can help steam the meat - and hold more moisture, a pork butt does not suffer from potential dryness that can affect other meats. The fat distribution throughout a boston butt, as well as it's thickness ensures it will be moist without foiling.
If you want to hang it to 200F IT - I recommend that you place the grilling grate in before you hang it - in the event that it comes apart as it approaches 200F.