I believe the white tentacles are generally considered a sign to the fish that they are a cleaner... as in, "Don't eat me, you need me!" That said, I'm sure a few non-cleaner species mimic this to avoid getting eaten as well.
I have heard of them cleaning rarely before. I've also seen a fire shrimp clean, but they spend a very significant amount of their time hiding (unlike skunk cleaner shrimp).