The acs5 at state level uses a gnis coding in query. maybe others do also. It is suggested that only FIPS codes, census codes (places, tracts etc), and OMB codes (cbsa etc) be used. folks are far more familiar with FIPS codes and it willl reduce a) confusion and b) Census resources to maintain a additional layer of geocodes. it might be that gnis is going to be a national standard, maybe, but we are not there now.
Idea No. 232