We know that one of Nemisis's other names is Lord of Slowest Terror. (Blood Rites, the chant that invoked He Who Walks Behind, who is said to be Lord of Slowest Terror's Right hand.)
Is Nemisis or Lachesis associated with slow terror? If not, it might put a crimp in your theory.
Or not. I just thought I'd point this out.
Still, I wouldn't think Nemisis (the Greek god) would be considered forgotten enough, to negate existence. So, maybe the Outer Gates don't have any effect on the Oblivion War.