It depends on where you have it and how many you have in there.
If you have it in your seahorse tank, it's bad. Seahorses can snick it up and die from the sting or choke on it. If you have a feeding station they will come out and crawl into it where your kudas can see them and think they are mysis. Or if you don't same thing, since any leftovers will be eatten up by bristleworms and/or other clean up crew members.
There good other then that just shouldn't be in a pipefish and/or seahorse tank.