You did say you had 'never' heard it.
I have heard it given to both VFR aircraft and IFR aircraft on visual departures (procedural airspace).
There are also plenty of SIDs that require a certain track to be maintained that is not coincident with any navaid whatsoever.
The phrases 'maintain runway track' and 'maintain runway heading' consist of nothing but standard phraseology so I cannot see why one or the other could not be issued to any aircraft regardless of the flight rules, flight conditions, or the licence held by the pilot in command.