I don't know.
You know I have some in both my tanks. While I've never busted them eating my "good" nems, the fact they eat anemone's at all, makes me wonder if they would eat any and/or all anemone's if they get hungry enough. I wouldn't add any to my tanks again. Just me though. I HAVE caught them stealing food from anemone's I have fed, but that's taking it out of their mouths, AFTER the anemone closes it's mouth.
If it was me, I would NOT add them. But, in a system that is doing well, with anemone's that are doing well, they most likely aren't a problem. Just my guess, which could be totally wrong.