I guess technically you might be able to say that EMT fittings are not designed or listed for use with NM cables, since I see where 300.15 says that fittings and connectors shall be used only with the specific wiring method for which they are designed and listed.
IMO, I don’t think the NEC allowing NM to be sleeved for protection was intended to allow unlimited use like that, but I’m also not sure exactly where to find a specific rule prohibiting it.
