Pyro I must congratulate you. I've changed my mind because of your explanation; now I read it like this:
These servants of the Dark, who were once human....
I had stubbornly hewed to the idea that these folks submitted themselves to the soul-stealing ritual of SB. But that rephrasing was all I needed. It makes more sense now.
Anyway, who in their right mind would ever submit to something that made you a slow-floating puffy little skull-head guy that smelled bad enough to kill? The "stolen" part imo means it was forced onto them. So they could have been hapless peasants.
Sure, it's more gruesome and depraved to think that poor folks are grabbed and turned into soulless than loser Dark human servants willingly submitting. But it makes more sense imo.
Thank you, Pyro!
-Welly