There's no mention of the Sith being a species. And when they say "the homeworld of the Sith" I view it as where the Sith were created. Where Force sensitives got together to practice the dark side and eventually created the "Sith", and possibly used Moraband as their base or whatever.
As for the Sith that were encircling Yoda, I think those were just guys in robes and masks. I don't remember entirely. Plus, weren't the Priestesses' conjuring them to test Yoda?