I have bristle worms in my tank and they never bother anything, just part of clean up crew. As far as eating the fish, I think they will only eat ones that are dead, kind of like what crabs and snails do. I have a melanarus wrasse that sleeps in the sand and I think if they were harmful, they probably would have eaten it by now.
In regards to that video, I bet that bugger is going to have a pretty hard time slithering back into his hole in the rock lol