Conquest of the Horde

Reading WoWWiki leads me to believe that troll priests can call upon both the loa and their own spiritual energy.

Quote:The Troll priesthoods are, much like the Shamans and the Witch Doctors of the various Troll tribes, spiritual advisors and caretakers. With Trolls being naturally supersticious and spiritual, it allows the various Troll Priests to manipulate the spiritual energy of the world in order to either heal or harm their targets. The various energies that the Troll Priests draw can come from various sources, be it Loa spirits, voodoo magic or the target itself. Drawing upon these energies, the Troll Priest either mend or harm, depending on which blessing the spiritual entity bestows.

I don't think we can assume that all the priests and priestesses of Azeroth operate in exactly the same manner. Most spells do seem to come from their own spirit, but others seem to come from outside sources.

Troll priests are very much like witchdoctors from my own personal findings. It is the Loa and such that empower thier vodoo, and from here the "good juju" as many trolls love to call it, manifests as healing energy. Similary, shadow magic is the wrath of the Loa, it manifests as "Bad juju" and harms beings that are touched by it.