Do I need DME or ADF in an IFR-certified GPS panel?

George Patterson wrote:
It's my understanding that the DME box in the plane measures distance from a
VOR. All VORs should be in the database.

Not all DME ground stations are co-located with VORs. Many are on
airports as part of an ILS-DME (and the exact location of the ground
station is not charted in that case).

If you look hard enough, you can find the occasional NDB-DME station.
I'm not aware of any stand-alone DME ground stations, but I can't
think of any reason why such a thing couldn't exist.