LOL... I got a few that are that size in my 55gal and they are around my clown gobies, neon gobies, and sexy shrimp. All have never been touched. When in doubt though, my advice is to pull them. Better to be safe then sorry!
I like my bristleworm. He must be pushing a foot. I consider him as important as any other fish..in fact he is my oldest fish in my tank since he came with my rock.
Personally, I would get him out. Eventually these things will begin to eat larger and larger critters in your tank and they pretty much don't stop growing.