Honestly, I think we should just have it in our lore that they're known to exist near slime colonies (Do those exist in our lore?) and keep them in. They're a nice way for ghosts to rejoin.
Also, they're useless because no one ever thinks "Hey, this flame proof, space proof, humanoid can be useful as a worker, lets make him a miner!". Off the top of my head, I can see them easily working as miners, engineering apprentices, botanists, medical orderlies, possibly as security cadets.
Regarding them being hassles. They can go down as easily as any grey-tider. They're not stun proof.