I can understand the annoyance because they leave behind a trail of closed zoas for me but they are cleaning them so I'm ok with it. If you were close to me i would take them
How did they kill the frags? Hermit crabs are scavengers; they rarely will attack a healthy item, but they will quickly devour an ailing (or dead) fish or coral
I would look else where, I highly doubt a few little hermits sabotaged your reef. You cannot have a reef without CUC, which includes hermits, Ive never had a hermit attack any type of coral, now Emerald crabs is a different story.