There are other ways. Vaelastraz had an interesting point when he/she mentioned those Ysalamir things. If neither one of them could manipulate the force, that might give Revan all the edge he needs. Have they ever been mentioned before in the Old Republic era?
The second lightsaber form was named after the ysalimiri, so one could only assume the Jedi Order at least was aware of them. Ysalimiri are frail creatures, though. All you'd have to do in a duel is find the ysalimiri and kill it -- it would take far more preparation than simply having an ysalimiri on your shoulder to make it an effective tool of battle. Of course then again Wookieepedia claims that Myrkr wasn't settled until 300 BBY, so who really knows.
The point I felt like I should bring up is that we've not seen Nihilus's power in action. It may be incredibly draining, or take incredible concentration (like Bastila's battle meditation). In fact Nihilus did devour worlds, but he did it safely from a distance onboard his ship. I somehow get the impression it wouldn't be an effective tool in close combat. Unless he can instantly drain all the Force out of Revan (which I doubt) Revan would have him cut down before he ever finished. As a result, I would assume Nihilus would resort to more conventional dueling techniques, where I'm sure Revan would be the superior.