you'll be fine, unless their fans tag the owner of video and the owner reports you, so out of respect put the name of the video and who made it in your caption, that way if you get caught you're less likely to get reported by the owner.
I very occasionally do it and havent been caught, but then again my pages revolve around sharing and crediting what people have made.
awhile back i was one of the first to post the new gymkhana video and that's definitely been seen by the creators and they didn't do anything