I think (to fomulate it carefully, because I'm no expert on this field) it could be possible to use such an Engine like Relic's one for RPG games, too.
I have one example in mind which could support this theory : Spellforce.
Spellforce uses the Krass Engine ("Krass" is slang used by youngsters to express "something is krass" - meaning more or less "extraordinary") known from the game "Aquanox" and "Aquanox 2" made by Massive Development.
The Krass engine, however, was highly modified and adapted by the makers od Spellforce, Phenomic , to suit their needs. As I recently read in an interview : "Well, at the core it's still the krass engine, but it is so higly modified that even the makers wouldn't recognize it." (Quoted from my memory.)
So Spellbound (and maybe Knightshift, too) is an example of how to use 3D engines for Adventures / Roleplaying / Realtimestrategy games.
