Could it be similar To Hungary with Horthy? The retaining of the Red, White Black, as opposed to the Swastika, might make the horrors seem normal.
I don't think the horrors would appear normal, especially a Germany that commits the mass murder, war and genocide that it did.
Yes, while we all agree pol pot was a genocidal maniac none talks about him really, yes mao was a the same as were many others. What set Germany apart, was that this was a white Anglo Saxon nation that didn't even try to hide being over the top whack. Let's take all the whack we can find and just go full tilt. Even today on this site there is little talk of the Japanese vs Nazi Germany. Nazi Germany set a bench mark for holy crap that's just so crazy that even the other nations doing crazy dumb stuff stop and say .. holy crap.. then said nation has truly flipped it's bit.
The soviets were horrendous, park that next to Nazi Germany ... etc.. they set a bench mark for planned barbaric behaviour that makes everyone pause and ask just how drunk are they?!
Even horthy was but a dreamer to the scale of what Germany did in 15 years. And again we are talking Germany, the cradle of empires, the land of enlightenment and education , the efficient Prussian machine.
There was no way after world war 2 and all the horror the went with it, to, normalize the camps, the mass murder.
You can normalize authoritarian, you can normalize racial inequity, but full scale industrial murder, that's a rough one.
(Rant off)
Now to the other part, a Nazi Germany that allowed to be pro monarchist ( Hitler wasnt a monarchist btw) would be a different Germany. The Nazis did use imperial colors when it wanted to, hell the Nazi flag uses the same colors.
Hitler also comes from no special background to be respected by monarchs , his rage and lack of trustworthyness is another item that would exclude him from a gentleman's club.
A Hitler who would now to a monarch won't be the Hitler we know and you would need to change things enough to make the monarchy and willy or the crown prince popular enough, or find a replacement of enough royal character to suffice , to again make things vastly different.
The Nazis wanted not just the return of the German empire .. they wanted mainland Europe , and all Germany. Peoples under the banner of the reic, and everyone else to be slaves, dead or if they were lucky while not considered German, they wouldn't be untermenchen
Btw .. I'm pointing out the obvious .. and not trying to pick any fights, I agree it's not hard to imagine in many ways, but the monarchy and Hitler/Nazis don't compliment each other, not could they tolerate each other, nor would they. You're pod needs to start very early and that change would change Nazis all together .