Nope, I don't think the clown gobies will eat zoas. I have never heard of this ever! I've had several myself and never had a problem. I think the guy who said they eat zoas, unless some recent rash of zoa-eating gobies has come in to the fish markets, is a total loon. I mean have you seen the size of a clown goby's mouth? It's tiny!
I guess you have those really small zoas and no food EVER it's possible. But I didn't feed my tank for about 2 years (before I got a tang) and mine never ate zoas.
Did he mean all gobies or just the clowns?
Disclaimer: if this turns out to be true, it will be ME who sounds like a loon.