Why must he be Shor? There are so many different warrior gods in Arena Mundus: Reman, Shandar, Stuhn\Tsun, not speaking of Yokudan spawn of war-gods.
And though Ebonarm is Nordic in origin, he seems to have a great influence in at least certain parts of Hammerfell and High Rock, too.
I tend to assume Shor because he is Nordic in origin, and while he may have importance in some Redguard and Breton towns, pre-Septim era those regions would usually be in flux, either by trade or war, so a lot of culture would move about.
And prow, I know he's not been mentioned since Daggerfall, but it could be that we simply haven't seen a province where he would be mentioned since then. If TESV is in Skyrim, and he isn't mentioned once, I'll never speak of him again. But if even one person mentions him, I'll assume he is at least a minor cult.