If the question is what inspired the Nazi's to carry out the Holocaust, then is it not of primary import to look at the words Nazi leaders used to justify mass murder to the masses? Not secret notes unpublished during Hitler's lifetime, not what secrets lay deep in Hitler's heart; what words were actually used to inspire and justify the Holocaust.
Eugenics was justified in the last century due to the misapplication of Evolution to think that somehow natural selection was not at work among humans (it is); however Eugenics was practiced long before Darwin ever published.
Saying that Eugenics was dependent upon Darwin (rather than just seeking justification under its auspices) is like saying that selective breeding of dogs was dependent upon Darwin; ignoring that the principles and concepts of selective breeding were well known throughout human history. Eugenics is nothing more than selective breeding of humans, and selective breeding has been going on for many thousands of years of human history.
The NAZIs used whatever was necessary to justify what they did. In the end it was a stew of racial bigotry, nationalism, economics, Darwinism, religion, jealousy, and a whole slough of things that led a supposedly civilized country down the road that Germany took.
Selective breeding was around before Darwin wrote his thesis. That doesn’t change the fact that it and Eugenics are still human controlled evolution. Darwin just put a scientific name to the process. Gravity existed before Issac Newton “discovered” it.
I did fly by your “evolutionary rhetoric” tag, I will admit. It’s late Friday afternoon, and a payday to boot, the mind isn’t too focused. Anyway, there is enough evidence to put rest to the thought that Darwinism/evolution didn’t have a hand in the NAZI scheme; everything from Hilter’s writings to school curriculum is there to see.