I'm thinking, at least for normal instances, that there should be enough dps to be able to burn down bosses fast enough that it shouldn't matter that you don't have a formal tank much like 5x shaman. I'm not sure on how healing works as moonkin as I have never once specced into it but does Moonkin limit a druids heals in anyway? If not I would imagine that 5x Moonkin should be able to do heroics. Even if not yea I think one feral would work out well as Feral still puts out some pretty good dps.