the spices in seasonings are soluble in oil but not water. thus, they break down and release more flavor. after cooking for many hours though, not sure if it makes a diff. vinegar is an acid and 'cooks" the meat slightly, like a ceviche, again not sure if it makes a diff.
with that said, i use peanut oil on ribs(i can taste that nutty flavor and like it), and a mustard based slather on pork called hit me fred by pitmaster t, no wait, the resurected barbefunkoramaque.
-In memory of a friend.
avatar by grillman. patent pending.