I think the better question is can Chop swim. If not I hope I can load him into the submarine and still take him with me.
This actually makes me hope there is some form of animal spawning cheat. I'd love to be able to spawn a bunch of wildlife in downtown LS to wreak havoc, or spawn a bear on a tall building and shoot it off.
As for the swimming thing, I honestly wouldn't be surprised if he was the weakest swimmer of the three. Whether it perpetuates a stereotype or not (honestly, GTA does that a lot on purpose anyway), it's usually true that inner city people aren't that great at swimming, black or not.