[CaptainCrunch]

I doubt it, he's a pretty powerful dark side user, but he probably isn't educated in the ways of the Sith.

A third Sith would be a path to power that neither Vader or Palpatine would want.

he's basically a useful tool for the true Sith Lords, and even though the EU spent years pooping all over the rules of two with secret apprentices (Force Unleashed) and Sith Acolytes. I would expect that Palpatine would be a Banite Sith and use the rule of two to continue the lineage knowing that Vader would probably never defeat him.

It is interesting that in the first episode Vader was talking to the apprentice about hunting down force sensitive children to use or to die.

Seems like Palpatine knows that there is an jedi threat.

the other thing that I took out of that episode, I have a feeling that Kanan isn't much of a jedi and he even knows it and the inquisitor knows it, especially when it comes to teaching Ezra. Its likely at some point in this series one of both of them flirt with the darkside.