Yes, and no.
The Sith were a race, a rather primitive one at that. Then there was this group of maverick Jedi that had been cast out from the order because of their crazy ass dark side beliefs. They fled to the outer rim, where they encountered and conquered the Sith, and appointed themselves as rulers of this race. Thus, you have some half-breeds, such as Marka Ragnos, that were part pure blood Sith, and part something else. That is the "true" Sith empire.
What I don't like about this is the naming. I mean, if those guys are the "true" Sith, that would make Revan, Malak, Palps, and the rest of the gang "fake" Sith. That's just lame. "Old" Sith empire would fit much better, without implying that the Sith we know and love are just wannabes.
That's garbage. Anyone licensed by LFL to write a story in the SW universe must first present any ideas to their "canon committee", or whatever, and must count with their total approval at the time of release. If the committee doesn't like something, then that has to go. So, GL isn't really that concerned about continuity issues as you might want to imply.