Not that I claim to know more than Pope Benedict's first-person Nazi expertise, but his claim that Nazis were about atheism is somewhat bizarre:
The Pope used this speech to warn Britain about "aggressive forms of secularism" and "atheist extremism" in society. He recounted Britain's stand against the Nazis, then stated "As we reflect on the sobering lessons of the atheist extremism of the Twentieth Century."
In a few short sentences, Benedict threw down a gauntlet by linking the atrocities committed by Nazi Germany with atheism. While, to be fair to the Pope, the Nazis had no real love for Catholics, Nazi Germany was a religious state. The Nazis drew upon both Christianity and Pagan influences. Nazi paraphernelia proudly proclaimed Gott mit uns (God with us). Nazi propaganda routinely referred to political enemies as atheists as a means to vilify them, and Hitler himself is reported by at least one close aid to have confirmed his Catholicism late into the war.
Not only has the Pope bought into the lie that the Nazis were atheists, but apparently he has forgotten the history of an organization he was part of, both as a member of the Hitler Youth and as a member of an anti-aircraft gun crew.
Speaking the lie to the Pope's claim are the various Nazi artifacts with Christian iconography and messaging on them.
Perhaps the Pope should have talked about Stalin. After all, the Soviet Union was an atheist totalitarian regime. But perhaps Stalin did not suit the Pope's purpose for various unknown reasons.