[quote=KabenSaal]
Sorry for being so question-y, but bringing up the Gurahl has opened another problem. How does their Umbra mesh with the World of Dreams?
[/quote]

I haven't read the WoT series, so I don't know too much about Tel'aran'rhiod, but from what I've read of it, it seems different from the Umbra. The Umbra can been considered as a pocket Spirit realm whose existence and inhabitants are intrinsically tied to the physical realm (i.e. Destroy the Penumbra, all life on earth dies. Kill the celestial, Luna, and the moon dies. Kill the spirit of an individual tree, the tree dies.) and while Tel'aran'rhiod can be reached through dream, the Umbra is typically reached through meditation, creativity, etc, during times of consciousness.
Also, what happens in the [i]physical[/i] world affects the Umbra (Sites of Concentration Camps creating hellholes leading to the Atrocity Realm) whilst what happens in Tel'aran'rhiod seems to exclusively affect the physical realm.

From what I've read of Tel'aran'rhiod, it seems that it links all possible realities and timelines, so it would probably make sense that a world that contains the Umbra is one of those possibilities. As the Gurahl noted when their Hex appeared, they were stunned that the world could sustain life without a presence of Umbra or spirits. They even thought the sun would die, because in their reality it would have.

So Tel'aran'rhiod is a world that even the Gurahl, Umbra spirits and Celestial do not know to exist. So, all in all, I'd say that the Umbra is merely a single possibility, found solely in it's own reality and capable of spreading throughout this new world, whilst Tel'aran'rhiod is a realm found in [i]all[/i] realities, linking them. 

I hope that makes sense?