I know that's technically something that the writers never had in mind, but it kind of makes sense. Going with the RP guides, the Prophets of the Dark Side did not totally reject the Light Side, and though a seuparate order, they seemed to serve as custodians of the Sith, especially when Darth Sidious came along and made it so that the Prophets and the Sith had a symbiotic relationship. The Prophets of the Dark Side would maintain the Sith by means of teaching them more about the Force and giving them helpful prophecy so that the Sith would stay around, and in return the Sith would pretty much give them jobs and intefere with the affairs of the galaxy in a way that the prophets were generally down with. Vergere is not totally anti-Light, and she does maintain the galaxy as the Prophets and the Sith would prefer by means of interfering with the Yuzhan Vong, and she does maintain the Sith by essentially help restoring them through Lumiya and Darth Caedus, which is what a Prophet of the Dark Side does, besides of course prophecy for the Sith. That was never the intent, but it kind of makes sense. I like to think of her as a Prophet of the Dark Side, who served under Sidious and Kadann but never meant to wreak complete and total havoc if she could help it.