The head injury is a great point, and to keep the timeline interesting, I definately support it as being a segway fot the Red Baron into politics even if he was historically resident.
So, supposing he gained some of Hitler's traits but not all of them? Megolomania, desire for ultimate power? Probably anti-semeticism, but his aristocratic background means his anti-semeticism probably wouldn't reach to the level of Hitler's. (Would Einstein emigrate, if the Jews were merely talked about badly behind their back rather than targeted for de-propertizization and execution?)
Anyways, there's a least a small chance of a Monarchal Restoration. If Richtofen realy is a Hitler analogue, maybe he has himself declared Kaiser in the 1930's. (He war relatively minor nobility, if I remember correctly, so he might have to rule as a furher instead.)
Nevertheless, being the best Ace in history up to that point...at a time whne air combat was still viewed as chivalrous...coudl have major reprocussions in history. For instance, I wouldn't post war Britian think of him as a Gentleman rather than an upstart....even if his policies were largely the same as Hitlers?
I could see Richtofen giving a speech saying "This is the wrong war" and the British public actually listening to him....maybe I'm wrong....but his aristocratic background and service in the most aristocratic and "chivalrous'' branch of service surviving into the modern era couldn't help but help, not?
Either way, if we get Manfred into policial power, I doubt WWII would happen as historical. I think he'd have 1/3rd chance of pushing for Anshluss, 1/3rd chance of taking checklosvlokia....and 1/2 of 1/3rd chance of pulling of Poland withough starting war.....and near a 1/3rd chance of backing off before poland. And if the war does start...I could see a larger chance of negotiated peace....and very little chance of holocaust/total war/no negotiatins/Manfred being hung at the end or committing suicide.