Simon Pietrovich being a member of the Black Court. That is an interesting idea. My only problem with it is, I think it was stated in Summer Knight that it was an inside job. The Red Court didn't breach Simon's defenses, someone let them in. So, that would mean one of three things, either (1) Simon was turned by Drakul first and let the Red Court in, or (2) Simon had some kind of deal going, let the Red Court in and was betrayed and turned over to Drakul or (3) someone else on Simon's team was the traitor.
The problem with 1 is, how would Drakul get past Simon's defenses to turn him? It seems unlikely if not impossible. Number 2 is doable, but it's complicated. It's got too many moving parts. Occam's Razor doesn't like it. Number 3 appears to be the most likely solution, but unless someone we know was with Simon at Archangel it would mean some random nobody betrayed Simon and the Brute Squad.