Concur with Soliton, the idea of selective breeding goes back far before Darwin, who merely observed that populations experience natural selection in the absence of any human interference.
Hitler’s statements rely heavily upon human breeding of plants and animals to produce strains with collections of traits we consider desirable, and the dilution of these traits upon interbreeding of two different strains. There is nothing about, say, labrador retrievers that make them “better” than huskies, but a human might object to interbreeding the two strains since the offspring probably would combine traits in ways we don’t necessarily desire in a dog. This says nothing about the inherent value of the offspring (labrahusky?), it’s a human opinion based upon ideas that might or might not be defensible.
The observation of natural selection (slow rabbits get eaten!) is insufficient to draw conclusions for moral behavior. Attempting to do so is illogical and irrational (see Hume’s guillotine). Hitler did not base his motivation for eradication of the Jews upon the premise that ‘slow rabbits get eaten’, but upon the religious notion that his race best typified the image of God, so breeding with other lineages would dilute desirable traits and debase the image of God. This, IMO, is an indefensible opinion.
This is why Hitler praises "the Creator", but never mentions Darwin.