Regals and Powder blues will eat certain corals. I've had both and both ate not only xenia but frog spawn and candy cane Needless to say..they're gone now.
Watch the fish closely... you will catch it in the act if it's doing it.
I'm in the same boat as you min.
If I oculd get a fish or something that would eat xenia and no other corals I'd be all over it (except maybe it could eat aiptasia as well)
I have a lifetime supply of xenia for my store now.
I have a French angel that can't swim past pulsing Xenia without having a nip. I think the movement is just too enticing, not that the fish has any real appetite for it.