Bittle stars are generally peaceful to corals...however they are nocturnal, so you won't see them much during the day. They are scavengers...they eat detritus and such...you can also feed them krill.
Linkia stars are peaceful, but I've been told they are difficult to keep.
Stars are very sensitive to changes in salinity, temp and pH, so keeping them in a nano 'might' not be the best idea given that there's not a lot of room for error, however I'm sure that someone is doing it successfully.