In that respect, absolutely not- the films are very clear on how many people the Sith will accept in their number.
In other respects I am flexible with EU; I'll judge case by case. For example, ysalamiri and cortosis are out, Darth Bane is accepted as the last of the great Sith Lords but the his plot given in the EU does not tally with GL's words on the Sith so I glaze over that bit, the plot of Knights of the Old Republic I am broadly happy to accept fully.
I would love to play in KOTOR aftermath, when both Jedi and Sith Orders are decimated and in total chaos, it would allow for much freedom and not being too much restricted by canon plot.
Ushgarak, have you ever wondered what would happen if Sith have managed to win one of those ancient wars?
I have always seen a system based on Houses/Clans totally engaged in both external and internal strife on a galactic scale, who has read anything about Drow society( it is Dungeons and Dragons fiction)?