[Mithadan]

This thread has moved very fast and there are some truly excellent posts here. Pitchwife correctly identifies Morgoth's Ring and specifically Laws and Customs of the Eldar as a source of information on the Feär, the souls or spirits of Elves (and Men) and William Cloud Hicklin helpfully quotes portions of the relevant sections. In addition to the excerpts addressed by William, Tolkien mentions the Summons of Namo (Mandos) which is intended to gather the Feär of the Elves into the West. Some Elvish Feär resist the Summons due to reasons mentioned in William's quote and some directly or indirectly respond to Morgoth's Counter-Summons. These Elvish spirits can remain "unhoused" or take over another body. It is unclear if the Feär of Men are subject to the counter-summons as they are fated to depart from Arda at death. Yet these sections of Laws and Customs seem to make up the backbone for what Tolkien considers to be "necromancy". Sorry Bethberry, I don't think he meant a reference to the general dark arts.

Formendacil makes a great point that there appears to be virtually no direct textual evidence about the reasons Sauron is named the Necromancer in his Dol Guldur days. We cannot attribute prior knowledge of Sauron's apparently known Necromantic tendencies to this nickname because Sauron's identity was not known. This begs the question of why the Wise did not identify the Necromancer as Sauron on this basis alone.

As distastful as it may seem, the Silent Watchers were likely animated by corrupted Elvish Feär. The Barrow-Wights? Likely the same. Werewolves, Vampires, perhaps even Dragons? Elves or minor Maiar. Sauron was certainly busy. But what about the time he inhabited Dol Guldur and what textual evidence exists of his activities? Well, William does mention Sauron's connection with Werewolves. In the Hobbit, there clearly are some sentient wolves; the Wargs. Even later, Gandalf, after the attack by wolves upon the Fellowship, seems to ascribe to those wolves a preternatural quality.