I think its going to be some of both. If the coaches have spare laying around at the end of the off season they can give it to a walk on. They probably start with either the most needy or the ones closest to contributing in a game, or actually contributing. after that it becomes a value engineering exercise. Is that walkon worth the continued scholarship? Dayne Davis probably kept his if I had to guess, but some other other walkons may have lost theirs or seen them "given" to another walkon who passed them.
I don't see either case, keeping or losing the scholarship, as an issue. and I don't see why it should be an either-or case.