Animalpower, in Warcraft, necromacy is a form of arcane energy. The naga are very adept at using the arcane. Now, even though we're creating a story (hopefully in a never before seen continent (magically hidden?)) it doesn't mean we can't reference to specific events in the past. The Sundering, for example, could have a significant impact on the magical powers the inhabitants of this continent have. The Necromacy may be specific to a cult, as magic isn't race specific. Anyone can become a druid, shaman, warlock, or mage. The same goes for necromacy. Now, what they have in Warcraft is just for gameplay mechanics, otherwise everything wouold be the same, except for racial abilities.
I do seem to have a lot of magic examples and varieties in the plot I'm creating, so we'll see where we can take this.
And as e've discussed before, we don't want to focus on what's canon. That would require knowing everything about warcraft, and how everything effects everything else.