I don't think so. The Emperor is metaphor-Hitler, not literal Hitler.
To make sense of the Emperor having been Hitler and then going on to be the Emperor, he'd have needed to come to the realization that all humans, Jewish or Aryan, white or black, man or woman, are equally human and worthwhile AND THEN utterly fail to in any way extend that logic to xenos.
There is also a mismatch of power-level; with the Emperor's abilities as described, if he'd set out to kill all the Jews and have Germany rule the world, he'd have succeeded.]
You know what major world figure in the 20th century might have been the Big E? Kennedy. Think about it; averts nuclear war, displays huge natural charisma, then dies under slightly odd circumstances. Big E stepped in to take the reigns of the world's mightiest country for a time, fucked Marilyn Monroe, then faked his death when the job was done.
That sounds a lot more like "At times of crisis he would be there, steering the human race along a narrow survival path that he alone could see" than taking power in Germany, waging a devastating but unsuccessful war and committing a horrifying but unsuccessful genocide.
Hitler did very little of what he set out to do. Big E tends to be more effective.