This post may contain spoilers for people who have not read all of WoT, Dune, or Mistborn.
I would have to agree with Todd. Shadar Haran is the avatar of the DO, so I'm fairly positive that if he manifests that will be how. Fain on the other hand...he's like Paul from Dune. Where Paul wasn't the Kwisats Haderach (sp.) he was something different. Fain is the same idea, in my opinion. He's something outside the archtypical good vs. evil battle between the Creator and DO. I don't think either of them had anticipated Fain. And quite frankly, I am awash with excitement to see what part his "otherness" will play in the end. I see an interesting correlation between Fain and Vin from Sanderson's Mistborn. She had that "otherness" quality as well. Not quite the Hero, but still "special", especially since she was Preservations tool against Ruin.
Although Vin was naturally inclined toward good, and Fain was "claimed" by evil. Still, I've been noticing these similarities in a lot of the stories I read. Once upon a time I would have thought this "cheap" on the authors' part, but now I just think it is neat.
Anyway, sorry for the ramble.