The pics are really hard to see what it is. It is however irritating your zoas. I would scrape it or cut it out. If it does not retract, it is not an anemone of ANY kind.
Is it soft or hard to the touch? It almost looks like a type of sponge.
if you can, take the rock out of the tank and see if you can get a better pic? Zoas can stary out of the water for quite a while. You might also want to dip them in coral Rx or melafix to clean them up a little.