It is not a guarantee that they will go after anything, but it is possible. I had one green that was a nuisance, knocking over corals, chomping on fan worms, etc. Had another green that never bothered anything...last one was a red emerald, and he wreaked havoc. He chopped up a small lettuce nudi, clipped the frills on another, killed ALL of my fan worms, and mangled my blue tang while it slept. It has healed up now, but has no left side fin anymore.
First chance I got he was gone. Personally, I won't get anymore unless somehow my tank becomes overrun with algae.
Just keep an eye on them, and keep them spot fed. My tank is 100g, and I only had one in there.