Asajj as a Sith?

Plageuis himself acknowledged that all Sith Lords after Bane always kept in mind more than once apprentice to replace them. Ventress is a bit tricky. Dooku (Darth Tyrannus) was obviously the true apprentice of Palpatine after Maul "died". Throughout the history of the Sith, the apprentice would always keep an eye out for other apprentices for when they themselves became the master. Palgues's master had more than one apprentice himself as well in case he needed to replace one. The rule of two is more of a guideline that an absolute.

This being said, since Savage is considered a Sith due to him being Dooku's apprentice leans towards the idea that Ventress should be Sith as well. I guess the only argument against this was the Dooku was using Ventress as an assassin with the prospect of becoming his actual apprentice in the future. This is why Palpatine had him try to kill her.