The real question is, what do you want the dead raised for? It's already pretty well-established that you can't bring a person back to life and have them be the exact same person they were before, but... maybe that's not all a Dark wizard is interested in. Do they want animated bodies for some gruntwork? There's already Inferi. Maybe information from the deceased? Perhaps some spell that's a dark variation on the magic portrait-making spell that brings the body back to life as a grim facsimile of its former self for a few moments. What about just horrible Dark magic in general? Maybe the darkest of dark magic has the power to bring the body back to life but not return the soul - possibly the Dark wizard has to shear off a part of their own soul to keep the corpse animated. The actual act usually isn't as important as the intent behind it, after all.