Not sure what someone meant by not needing an ADF for a non-precision. Dual GPS approaches are not yet authorised, so an ADF will need to be tuned and idented in such cases.
Nothing to do with GPS, however i suggest you check FCTM page 5.39 (Raw Data Monitoring Requirements). Raw data monitoring is recommended but not required both for classics (EFIS update 7.2 and FMC version > 7.1) and NGs. The MEL allows dispatch with the ADF inop as long as one FMC is operative even for NDB approaches.