Lord Raith has magical protection that Eb says may have come from a big demon, although he wasn't sure. According to Jim, Drakul didn't want the Black Court vamps to have huge numbers. He preferred a small, elite group of followers. (If memory serves. I don't like stating something as fact without the source link)
Here is what I think happened. Drakul had a problem. He didn't like the Black Court growing out of control the way it was. They were hated, feared, and noisy. They were drawing unwanted attention to him. He prefers to live in the shadows, and work quietly.
So he wants them to get cut down, but he doesn't want any of his loyal supporters to know that he's behind it. So he makes contact with Lord Raith, and cuts a deal. "You make public their vulnerabilities in a way that cannot be traced back to me, and I will grant you protection. Or you could refuse and I will kill you"... Easy decision for Raith.
This is where I think Raiths magical protection is from, Drakul.