I for one have not been reading this on the assumption that an ATL, leftist Hitler must automatically by some conservation law be as wicked as our OTL version. In principle, Marxist thought ought to free him of his own mind-forged manacles and racial prejudice of any kind. Of course in reality many Communists have managed to remain racist anyway, to their shame, and we are after all dealing with a Hitler who diverges at a rather advanced age. So yes, the odds are high that he will use Marxism to rationalize basically racist programs. And that he remains a petty asshole who will nurse grudges and seek revenge on anyone who slights him, though it may take decades to get into position to do that. Such pessimism seems all too realistic.
But his leftward turn remains an opportunity for him to gain deeper insight and learn to rise above his worst nature, and I don't think a TL with a reformed Hitler is out of bounds.
Since the real OTL Hitler was so very odious, and his latter day fans remain so dangerous, we might want to avoid stories humanizing him, for reasons of expediency. But in principle, I think it is a shame many assume he must be wicked and despicable in any possible TL.