Here's a paper with a little more complete answer. A good idea to read the whole paper and get the framework, but I can understand jumping down to the "important part". Look down at the top of page number "89" for Gobiodon citrinus (it's actually page 17 of the pdf). You'll see 99% of its gut contents were Acropora polyps. So, if you're keeping everything else but Acropora you're probably in good shape. If you have a lot of grown out Acropora, again, you're probably in good shape if you don't mind retracted polyps and it browsing on them. If you're trying to grow out small frags and only have a handful - not a good idea (yes, I learned the hard way a number of years ago when I had one strip a handful of frags before I could relocate it).
Other members of the Goby clan don't appear to have this specific of a dietary preference/requirement, so if you plan on keeping acros, I'd recommend another choice. I kinda like the Gobiodon atrangulatus - Green Clown Goby, as it pretty much stakes out its territory in a coral head and fends off any intruders. Others out there a pretty cool, too.
Might want to skim this paper for any planned purchase down the road, too. It can at least provide a starting point for a purchase decision.
Hope this helps a bit.
Cheers,
Ray :cool: