Whoa long thought provoking read and a coffee later...I never looked that deeply into the connection between those two. It does sound totally plausable that Nihilus was the DS twin of the Exile and maybe Nihilus face wasnt shown as its a plot twist thats waiting to be revealed in K3 or just too similar to Revans Dark Lord reveal in K1 who knows?!
I was always under the impression that Revan was The Exiles opposite. Vrook says something about Revan being the life and the Exile being the death of the force and along with the The Exiles hazy 10 yr memory I dont quite buy the fact the The Exile is a good guy or will be in K3.