No one seems to think of the possibility of it not being Revan. If you remember the end of the revanite story line on DK then you'd remember that they are willing to same Ravan is leading them, and have it be just some sith. Also he has a different voice from the one I saved, and thinking back it's more like the one on DK.
In short I would argue that the Revanites are just using the knowledge that Revan may be alive to fuel fear into there enemies and rally there allies.