Hey Chris! How are those frags doing??
I do not think an Entacmaea quadricolour will eat a Ricordea yuma . However, it may have caught flow and rubbed against the rbta...and/or got stung in a similar way. I am not sure, but maybe it died after that? It is possible that it is in the rockwork. I've had some mushrooms that disappeared on me on my last tank. When I took the tank down, the mushrooms were all over the back of the rocks, where I could not see them growing just by looking through the front acrylic panel.
Also, what did your friend say about the ocellaris?
Thanks,
Ilham