On a smaller scale. Sure. The Assassins in the triumvirate used Nihilus's version of Drain as well (Kreia states this), and yet it didn't kill, only weakened the victim and made the Assassins stronger. It depends entirely on how powerful the user is relative to their victim. Otherwise you'd be claiming Nihilus could kill the Ones of Mortis with that technique.
I don't think their drain is normal, but it's hardly "unique" either, and I don't need you lecturing me on KotOR II. Also, Kreia states in cut content that Nihilus may "even rival" the ancient Sith, which basically means some of the ancient Sith used it (after all, those teachings came from Malachor V, and the ancient Sith were there at some point). She does state at some point that the technique was lost since "the ancient Sith".
She also states that you can't use Drain without experiencing it first, which is interesting because I don't believe the Sith Assassins ever experienced being Drained themselves. Likewise, Revan and Malak learnt those techniques without being Drained themselves. That could well be just a plot hole like Traya managing to Drain the Exile in the DS version but Nihilus failing to (although it seems arguable that Nihilus's Drain was only blocked because the Exile was his polar opposite, but that's discussion for another day). Still, Avellone seems to have contradicted himself with his own writing.
Anyway, it doesn't matter. Traya hasn't shown a defense against normal Drain either, and Sadow and Muur are both among the ancient Sith, so it's possible they knew Nihilus's technique. Even if they don't use it out of fear of their personalities being consumed, I don't see why Kreia is exempt from that. She probably only used the Drain against the Masters as a rare event, as opposed to people suggesting that she would (especially in a morals on scenario) just Drain anybody she fights.
This is all moot anyway because Drain has been disabled in the OP.