The lack of a paper trail is one thing (which I really don’t think is tied to the Nazis being German, but anyway), as well as the only scattered and vague reference to a “Final Solution.” I think this was surprising given that other orders were oftentimes extremely specific, and I’m not sure how much fear of international condemnation really played a part masking Nazi orders.
I think someone else made the rather maccabre calculation of how many people could actually pass through the gas chambers, etc. And they came up far short of 6 million. Of course, I’m not really sure how they made that calculation, and they take the logical flying leap that the camps were built for other purposes, but never really provide an adequate explanation for why they were all there anyway.
I don’t know if it’s strictly tied into white supremacy, but of course that is an element. Check out David Irving. He’s the scholar that took another scholar to court for libel in a critique of his book on the Holocaust (that it never happened). What is shocking about Irving is that, I believe, he has no ties to white supremacists. Another interesting take would be “The Protocols of Zion,” a documentary that came out last year, I think. More to do with 9/11 conspiracies, but an interesting exploration of the underlying motivations and sustaining sources for these ideas.
But, in the end, eh. What are you going to do? People will believe almost anything, even when it’s been disproved a hundred times over. Hope this provides a bit more information.