Garmin has added localizer-DME waypoints to their GPS databases. That means pilots can use an IFR-certified GPS receiver in lieu of DME on all localizer, localizer back course, ILS, or any other localizer-type procedure that requires DME.
“FAA granted approval in 1998, but some localizer-type approaches were excluded.”
That’s because GPS databases put the airport waypoint at the center of the airport. DME transmitters are usually co-located with VORs or localizers, not at the airport center. Using fix distances from the airport waypoint would give a pilot inaccurate distance information for an instrument approach.