Don't judge me but one day we were having a child-related issue (I think a last minute super poopy diaper change in the cabin) and so I went to the dining room first.
My DH (who is super absent minded) came in about 10 minutes later wearing cargo shorts into Animator's. I glared at him, but no one said anything at all. He sat down and stayed down so no one noticed. So yea, I think generally you "can," but it's not polite since others will not be wearing shorts. It was Pirate Night so also more casual. I can't speak for Cabanas.