May I ask what kind of spirits you're speaking of? In most texts I've read that deal with the topic [aka: Dracula's library which is full of terrible information like this] if additional spirits are mentioned besides the dead themselves, they're usually demonic spirits from Hell itself.

[Alucard knows that his own book access is deeply biased, and so it is worthwhile to ask.]

In addition, how are you so sure that your system of magic, including necromancy, will include those same types of spirits here?