I don't think its a good idea, everyone should pay attention when the line moves up and watching a DVD might distract you and others behind could get testy. Lines are not that long and as others have stated, fast pass works on the longer lines attractions.
A DVD player, portable even, hooked up in the resort room is a good idea, we use ours this way, for the crappy TV stations in WDW. A good movie now and then on TV breaks the hum drum of the Disney cable, we use it every trip.