I don't think so, but if you're horse does happen to start, rub a bar of soap on the corners of boards and such where he/she tries to do it. It won't hurt then but the taste will make them syop
Yes they could watch another horse do it and learn how to
It's not contagious so it's fine. I know the barn horse isn't yours so it's not of your responsibility but if you think it's serious then tell the barn managers or stable hands the situation and go see a vet. But your horse will be fine.
Cribbing can also come from boredom so if the habit does begin try to change up something, such as more time out of the stall.
I personally do not think you should have any problems with your horse picking up the habit. It is not contagious so you should be fine.