I have had emeralds for years
I have not once since 2005 seen my emeralds eat anything other than food and algae.
I have seen them throw up their arms when a fish gets too close but never any harm.
I've always had Emeralds in my tanks. Never an issue for me but someone will chime in that's had problems. Like everything else in this hobby , there are no definites.
I had one that would fight over a spot with my Pom Pom crab. The Pom Pom always won and then he would have the spot. Never saw the emerald much anyways. Once a month id see the scuffle go down.
My emerald crab was part of the first batch of my cuc and I've never had problems with him, actually when I feed my fish with the turkey baster he will come out and I feed him just like I feed them .