Can hitting a dog with whip be abuse?

Actually, there is little to no chance that this would not be abuse - whipping an animal is inherently painful to the animal and does not communicate training or information to the animal (except that this hurts and to try to avoid doing whatever brought the whipping on, which the animal generally doesn't understand).

If you have seen this, I would suggest contacting the local humane society or dog pound as this may be criminal animal abuse and the authorities should be able to remove the dog from this situation.