That makes sense, just because you have two lightsabres doesn't mean you have to use them-Revan might have saved the two sabre style for hard fights. It is confusing though, since the only times you ever see Revan holding a sabre is in KOTOR and a flash back in a comic dealing with the Sith, in both cases He/she is only using a single sabre. (The Flash back of Revan in KOTOR 2 doen't count as it wasn't really Revan)
If I had to guess as to the form Revan would use with a single sabre I'd take a guess that it would either be Juno-Sith Lords Sidious and Maul used this-or Form V: Shien / Djem So, which was Vaders style.
Well it is Revan up to a point. It is from what the Exile knew about Revan from the Mandalorian Wars.