... You just took me to school.
While I do think that Dark Jedi do qualify as anti-heroes, I don't think that Light Side Sith can qualify as anti-villains. To be a villain, you, basically, must be the bad guy. Allow me to explain.
My Sith Warrior is Grey, and I don't really see him as a "bad guy". He's honest and loyal, he truly believes that Imperial order will make the Galaxy a better place. He treats his position as a nobleman with full responsibility and uses the authority of a ranking Sith to strengthen the Empire and to provide for its subjects. He despises Sith who succumb to their base passions, viewing them as a threat to the integrity of the Empire.
That said, he is not a wholly "nice" guy. A traitor dies, for such is the Imperial law. A Republic spy dies, for he is the enemy of the Empire. An enemy dies, because such are the realities of the time of war.
So what I'm trying to say is - despite how obvious this may sound, "good" and "bad" are kind of relative in ToR, at least faction-wise. Yeah, the Empire committed many atrocities, and many of the ruling Sith are corrupt. This, however, doesn't mean that there are no patriots who truly believe in the Empire's ideals and those who want to make the Galaxy a better place. Story-wise, our characters appear to be of a generation that had nothing to do with the initial war - and, basically, they work with what they have, according to their convictions and their moral compass.
I gotta get Krissie to read this tonite- we are so gonna end up debating!