Since nobody has commented on this I will. If I were you I would remove the skin just to be on the safe side. I have never fed squash to my rabbits so have no personal experience. I would air on the side of caution.
I have never fed squash to my bunnies ( I feed it to my fish and I eat it as well) If I were going to feed it to the bunnies I would wash it, leave the skin on and cut it up into pieces appropriate for the size bunny you have.