Looks like there is a lot of conflicting information out them about them (then again there are 10,000 different kinds of bristleworms). One source indicated they can kill fish, corals, etc. and they can multiply quickly...so if everything was doing okay, them maybe they are alright, but if things are coming up dead....I would get them out ASAP!
Here is a source that would seem to support the idea they need to go:
http://saltaquarium.about.com/cs/msubpestbworm/a/aa102198.htm
The name "bristleworm" is a label loosely applied to describe all Polychaete class marine worms, but it is members of the Fireworms Amphinomidae family that have earned the name of being what most aquarists consider to be "true" bristleworms.
Primarily it is the Pherecardia (Pacific), Hermodice (Caribbean), and other related species that one needs to be concerned about. These Fireworms are errant (roving) carnivores that can cause much damage in a reef tank. They bare toxic bristles on their bodies that can inflict a sting of a very painful degree, posses strong jaws for feeding, and can reproduce quite rapidly.
They are not selective about what they eat, but usually prey on all types of other motile (moving) and sessile (attached or stationary) invertebrates, such as corals, crustaceans, mollusks, sedentary type as well as other errant type bristleworms. Being particularly aggressive predators, they may even eat small fishes, if an opportunity presents itself.