The two are not mutually exclusive. He might believe that the Holocaust has been greatly exaggerated, and also (more privately) believe that it would have been a good thing if it actually had gone further. Given that most Holocaust deniers are by definition raving anti-Semites, I suspect this is true for many of them.

In fact, this is quite clear in the case of the more media-savvy fascist/white supremacist movements. They publicly deny advocating racial hatred or violence, while simultaneously railing against the "Jewish lobby," endorsing (implicitly or explicitly) Nazi propaganda, and siding with Holocaust deniers.