The butterfly effects would add up and and any zygote formed would not be the hitler-as-we-know anymore, since it would be a different combination of sperm and eggs.
Who needs guns when you got a time machine? Don’t like your highschool bully, just bump into their parents back in time. Or you know, “bump” ( ͡° ͜ʖ ͡°) into their parents.
Ehh, people are capable of doing pretty nasty shit regardless of sex or gender. But on the other hand, had Hitler not been a cis man, it’d have been a lot harder to get in a position of power that’d enable hitler to do what he did. So I see your point.