I say no.

I agree, he is a Sith, which has nothing to do with faction :) Kriea is also a Sith, yet she was made as a Fringe piece. Just because you are a Sith, doesn't mean you automatically should be in the "Sith Faction" in our game. The two are similar things, but not exactly the same. The Imperial faction is a "Sith Faction" and Vader belongs exclusively to it.

As for the Sep Vader, I agree, totally wrong - perhaps more so than a Sith Vader even. Even in his 15 minutes, he still believes he is serving the Republic/Empire and goes to Mustafar to end the Sep leader and the war in favor of the Republic/Empire.

The only issue I see, is that some people think this minor time frame (of which we have 2 Vaders already), justifies a Sith Vader. Vader was not acting in the name of the Sith, he was acting in the name of the Republic which he had agreed should be reorganized into an Empire. Hence, even this 15 minutes is him helping set up the Empire.

As for other figures of the time, Vader's Apprentice could be argued for a Sith mini, but I'd still put him in the Imperial faction. At least in this case, you had a figure working against the Imperials to a small degree, and Vader's involvement was only as Master - Vader still functioned within the Empire, using his new apprentice to work outside of it - which is categorically different than what Sideous was doing.

Just because Vader was a "Sith Lord" does not mean he belongs in the "Sith Faction". :)

All the Sith in the Sith Faction embody or follow the particular Sith Philosophy of their time.

Vader never really did.

Kreia was an outcast.

So I'd say no. Honestly, if the designers make one and it brings something fun and interesting to the Sith Faction without detracting(why you'll likely never see a Rebel Vader), you won't hear me complain. Same could be said for Dooku.

here is my take on it. Wotc Changed who the SIth were as a Faction by puting in Darth Maul and Darth Sidious. Vader was Primarily part of the Imperial Faction, but he is still a Sith lord and during the Imperial Era There were only 2 SIth. I think their could be 1 vader in the sith faction. I dont think thei9r should be alot because he was kind of the face of the Empire, but to me he is still a sith. thats just my opinion though.

I say no, and I think there are already enough Darth Vader figures. Darth Vader was an integral part of the Empire. I think the Sith faction should only exist for those Dark Lords who existed during a time when the enemy of the galaxy was identified as Sith. Palpatine I can agree with only because he alone revitalized the Sith doctrines for a new generation, even though he chose to call his Empire the Galactic Empire and not the Sith Empire, because he overthrew the Republic politically and not militarily as had been attempted in the past.

Hey! Maybe after the Sith Vader we can get a Rebel Vader too.

I think we need a Rebel more than a Sith Vader. Although he should be named Anakin, not Vader. The whole six-movie series is about the fall and redemption of Anakin Skywalker, but we have no mini to represent his redemption other than the Force Spirit. The mini should be a piece that kills one powerful enemy piece (representing killing Palpatine) and then dies itself, with a strong possibility of being turned over to the enemy via Internal Strife or something like it.

What he said.

No way.

Sidious, Maul, Lumiya and Caedus shouldn't be in that faction eith IMO

Preferably no. I like Vader as exclusively Imperial.

But the Sith faction is so scattershot fluff-wise it wouldn't be any worse than it already is.