Any crab shouldn't be considered totally reef safe, emerald crabs are pretty fish safe from what I have seen. They have never attacked any of my sleeping or swimming fish. In fact my sixline pestered my large emerald crab, I still think he became a meal for it when he molted. His favorite place to perch was in between rocks and lay sort of on his back while eating and picking at algae. The sixline would come up and grab a pincher or a leg. One thing about SW
tanks each animal has a purpose and a crab is usually on the clean up crew so if a fish is dieing or dead they will take care of it to the best of their ability. Just like a sixline is a born hunter and hunt for worms and anything else they can kill. Even corals are completely coral safe I have had one acan kill off about 5 heads of my candy cane, attack a duncan and bother a mushroom. I underestimated the length of his sweepers and one night he went on a murderous spree.
How long have you had your tank and wrasse?