Would Hitler have been a bad person if he had become a gay vegetarian artist instead of a dictator?
This question can not be answered as Hitlers sexual orientation, diatary choices or occupation can not be singled out as the reason for him being a bad person. It is of note that in his later stages of life Hitler adopted a vegitarian diet and still persuied art as a hobby.
I'm writing an alternative history novel, so this is a really important plot point: Who do you think he'd hook up with?
Since we're in the realm of pure speculation, might I suggest to try someone humorous? A member of his cabinet or someone he was historically opposed to? The leader of a political party or regime you don't like? The leader of a political party or regime you DO like?
Benito Mussolini could be interesting due to the nature of Fascist Italy's reliance on Nazi Germany.
Roosevelt or Churchill could create a bit of intrigue.

I'd go with Stalin as you've got a built in breakup story with Operation Barbarossa.