So the question then becomes "what marks someone as evil?"
If we break someone down into 3 parts we have:
1. Intentions
2. Actions
3. Results
There can be no denying that many of his actions and many of the results are evil, in the sense that he intentionally caused or enabled harm to fall on innocents. So we know that he does evil things and evil things happen as a result of things he does. So do we assume that evil/good is a scale? Do more good than evil and we simply ignore the evil? Or do evil actions/results taint the whole making him evil with some good actions/results? Then there is the highly dubious tactic of grading someone exclusively on their Intentions. Do we accept the "As long as he wanted good things to happen, all of his evil actions and results are forgiven" argument?
By the definition of philosophical hedonism, he would in that context be viewed as good, since the sum of his actions, both good and bad, result in the net gain of happiness across the board.
1. Vivec kills Nerevar and becomes a god through profane means. Bad-
2. Vivec forms Temple, giving structure and meaning to the lives of tens of thousands of Dunmer. Good+
3. Vivec convinces Dunmer to surrender to Empire, rather than be wiped out, saving thousands of lives. Good+
4. Vivec persecutes a small number of Dissident Priests to prevent them from destroying the faith. Bad-
We would have to make a listing of all his sins, but in the end we would find that Vivec, when performing his evil actions, performed them on a small number of individuals, as opposed to his good actions, which were performed on thousands of individuals.