I've never seen them irritate anything, I have thousands of them in my tanks, I have so many that sometimes when I clean my socks I cull a batch.
I find it hard to believe you don't have some in your tank already.
They are a healthy part of the ecosystem, their food is something elses poop.

well I have lots in the sump, but the DT is all dry rock, so I doubt if any have made their way up there, I would love to find a little bag of pods, brittle stars, and other life forms for up in the DT, the pods make it up from the fuge but I haven't seen any of the bristle worms or amphipods(not that I want those buggers up there)