Yeah, basically. It wasn't a very defined concept and was more of a broad magic type that had different "patrons". It made more sense (at least to me) than having "Death" (and Undeath as an extension of it) as an actual physical force in the universe (because this creates its own issues). Nathrezim for example were heavily tied to the Scourge because of their affinity for Shadow magic (because back then Shadow magic was what created undead).