The chippers I've operated with winches had an interlock, so that the feed wheels could not be operated while the winch was being used.
I've hired petrol driven capstan winches a few times for specialised jobs. They come in handy if you've got a bunch of trees down the bottom of a steep hill and no access for equipment. Dragging them up is impossible. A normal winch just doesn't have the finesse of a capstan, and is too slow to return the rope. Capstan winch works great for that kind of job, because it has a lot more feel than the normal style of winch.
For chipper work, I see no advantage that a capstan would have over a normal winch, actually I'd say the normal winch is better.
Shaun