I can't speak for other forks of rfm, but ginjo-rfm does work with Filemaker 12. Filemaker hasn't changed their XML api in a long time, so anything that worked in 9, 10, 11, (7 & 8 too?) will work with FM 12.
I did find what looked like a bug in the FMS 12 web publishing engine, when trying to manipulate FM accounts using script steps. I filed a bug report with FM Inc., but I wasn't able to reproduce it consistently.