It doesn't get any more basic than this: I just downloaded FM Go 12 to my iPhone 5 running iOS 6.1.3. It can see my iMac, which is hosting several databses in FM Pro 12, but it can't see any of the hosted files (no files available). "Don't display in Open Remote File dialog" is of course unchecked.
I think we can dispense with a lot of networking-related potential issues by noting that I've got FM Go 11 installed on the same phone, and FM Pro 10 installed on the same Mac. FMG 11 sees the files hosted in FMP 10 just fine. So it can't be a network issue, a firewall issue, etc.
I'm just wondering if there's a switch somewhere in FMPro 12 that needs to be thrown. I'm not aware of any sharing preferences anywhere other than in Filemaker Network settings. The settings in FM Pro 10 and FMPro 12 are identical, as far as I can tell.