I think Tolkein used it in the traditional sense where necromancy = black magic, not actually raising the dead (despite necro meaning death, traditionally going back to say, Christopher Marlowe's Dr. Faustus, it's just a fancy term for black/evil magic).
On the other hand, he created the Ring Wraiths by corrupting their souls with the rings and they are definitely undead shades, so I guess his name is apt in that sense. But, will we see Gandalf fighting zombies? I don't think so, awesome as it would be...maybe Sauron can dig up some
barrow-wights so we can finally get to see them on film, haha. I guess there are several undead monsters in the Tolkein-verse...