Dear heart, as has been pointed out Hitler got many of his ideas on race from Martin Luther. Additionally he was heavily influenced by Theosophy, a 19th century racist philosophy that has some modern descendents in America. Theosophy taught that some races were inherently superior to others -- but considered the lower races to be degenerate descendents of any earlier race, while the Aryans were closer physically, mentally and morally to this earlier race. Hence the Nazi obsession with keeping the bloodlines pure. Evolution never entered into it, and cannot be considered a contributor to Naziism.
I pointed out earlier, half in jest, that Darwin's work appeared at a time in history when England and the US were abolishing slavery, and that Darwin could be considered to be a cause of abolition -- and ultimately the civil rights movement. Upon further reflection, I think there is actually more to this than mere temporal coincidence.
There is a long section in Darwin's work when he considers the evidence, pro and con, about whether the negro was a separate species. Despite the almost universal racism of the times, affecting Englishmen and Americans (and probably the rest of the world too), Darwin refused to conclude that the negro was of a different species from the white man. In this, he showed remarkable intellectual fortitude, and his work can indeed be given some credit for our currently enlightened views on race. This is a much more defensable position than blaming Darwin -- by all accounts a gentle soul -- for the evils of Hitler.