This is the first time I've heard of it, and it doesn't make all that much sense as a solely German narrative to me. Germany was a relatively small colonial power, and they were by no means unique in the practice of atrocities. If the Nazis were to have drawn from an emphasis on racial superiority, it would be one that was prevalent across Europe, and not limited to Germany.

The British, French, and Spanish all had large colonial possessions and today their ill-treatment of indigenous populations is recognised by historians today.

The most well known example of the Spanish would be Christopher Columbus, and his initial exploration of the Americas with Spanish forces and on behalf of the Spanish crown. He literally worked native populations to death in the mines, murdered entire islands of people in his quest for gold, or even just for sport.

The British interactions with Native Americans are probably the most famous example of ill-treatment in their colonial history, but I'll focus on two other regions for a bit of variety. In Ireland, the British occupiers engaged in torture, murder, and genocide for over half a millenium. British "scientists" attempted to classify the Irish as a different (and lesser) race in the nineteenth century. They employed phrenology(measuring skulls) to do this, just as other psuedo-scientists did in trying to prove the racial inferiority of Africans.

The British were also guilty of what we would call human rights violations in their other colonies, but with specific reference to Kenya, these continued beyond the second world war, and thus post-dated the Nazis. If you search Google or The Guardian for articles relating to British occupation of Kenya and the archival record, you'll find several pertaining to the accidental uncovering of files that were buried in British archives to hide the record of these events.

All these cases of colonial violence outside the usual realm of warfare were justified by a concerted belief by those in control that they had a right to do this. The Spanish were gifted the lands west of a certain point by the Pope, and as such, they took the inferiority of non-Christians for granted. Even when native Americans converted to Christianity, the Spaniards felt no compulsion to relax their sprees, justifying the killing of new converts as a quicker way to God. The British, as evidenced by their Kenyan cover-ups, were far more adept at "cleansing" the historical record so to speak. Records survive from across their empire however that show feelings of superiority to colonised peoples. They were nicer to some groups, of course. The Maori in New Zealand were described as "brown-skinned Englishmen" by some, but context also applies here: New Zealand was colonised far later than other regions, and undoubtedly this influenced how Maori were treated.

So to summarize, the theory doesn't really hold weight in a national history, because a narrative emphasising racial superiority wasn't unique to Germany - it was a generally held belief in Europe. However, Nazism drawing on that wider European view could work, especially from the point of view of drawing other European nations to the cause. Except, we know it didn't work out that way, and in fact, the major colonial powers either opposed Germany(Britain, France, America to an extent) or remained neutral(Spain). That is not to say there weren't supporters of the Nazis in those countries. The Vichys famously sided with the Germans, and Oswald Mosley was a supporter of Hitler, as were many in the British upper class. Notably, that upper class supplied the politicians who guided colonial policy in previous centuries.