Well, Dawn Eden's comboxes are certainly gettin wild! I think we need to establish a few things, so we all have an understanding.
1.) The Holocaust freaking happened. Whether it was 6 million or 10 million or whatever, millions upon millions of Jews, as well as millions upon millions of non-jews, were systematically murdered because they were not of the master race. Hitler saved his largest perversities for the Jews. This is a historical fact.
2.) From a purely 100% academic standpoint, one could wonder if the Holocaust occured and still be a Catholic.... I suppose. Technically speaking, it isn't in the Creed or revealed dogma.
3.) One could also be a Catholic and state the world is flat or only 7,000 years old. You'd be a moron, but you could still be Catholic.
4.) People would be right to conclude that even though you are free to be Catholic and hold this view, something is deeply wrong with you, since you need to resort to the worst of conspiracy theorizing to hold your view.
5.) To act like this is something Catholics should just ignore because "it isn't of the faith" is just dumb. It asserts that historical facts copiously documented by all parties involved should be placed on the same footing as the racist musings of crackpot historians.
6.) Finally, internet traddies of the urine and vinegar wing, wondering why nobody outside of your little enclaves takes you seriously? You guys are arguing over whether or not one can(or should) deny the Holocaust and still be Catholic. The rest of us are too busy working on promoting the Latin Mass, actually teaching the Catholic Faith, and evangelizing.
If you've gotta talk about this crap, cut off your internet connection, go to the gym, and go to adoration, and preferably confession. Other than this post, I'm done talking about this nonsense.