I agree totally with your appreciation of Oblodra's voice. She's enthralling.
The voices of the undead Shar-nurses in the House of Healing were also a jewel. But maybe that effect comes from the sharp contrast between the voice and who is using it.
I think Oblodra is a real Drow not a demon , because I heard her mutter that she will restore house Oblodra to glory.
Oh yeah, those nurses. 'Are we poorly? Are we desperately poorly?' Yeah, they're cool. Would've been cute in life but now the deathly visage makes them shocking. Great design and dialogue. And there's that funny scene should you act sick (another check fun to fail).
I've got a bias. I don't kill them, nor the female mummies. It's probably not healthy.
Okay, Oblodra's probably drow. But I reckon she's going to end up a yochlol.