There are certain species that have been known to eat polyps and such; however, you more than likely do not need to worry about these as they seem to appear rarely in the hobby.
Also, some people will recommend a coral banded shrimp, or pair of them, to help maintain your bristleworm population. I didn't have any luck with mine hunting them down, he just scared all my fish and wouldn't let anyone on the left side of the tank.
I did have an arrow crab, he worked great. It was pretty gnarly to watch him take a worm in his claws, twist it out like a wet towel and eventually start plucking it to pieces. Sounds mean, but it was quite enjoyable to watch at the time.
A homemade trap that I made was fairly successful, but I also "caught" a lot of my nassarius and blue legs in the process. I used the panty hose method. You place frozen food in the hose, tie it and weigh it down to the sandbed. Place it in the tank overnight and it should attract bristleworms. They get stuck in the hose and after a few nights of doing this you'll have a nice collection of bristleworms to give a fellow reefer, or to do with as you please.
