The real reason the libs hate the Nazis is not because of the Holocaust but because they stabbed their good buddies the Commies in the back, after using the security achieved by the Hitler-Stalin Pact to launch the war in the first place. For years and years and years and years we've heard about how the poor Russians bore the brunt of Nazi brutality and did the job while ee-vil racist America was fighting quaint, non-western Japanese. They don't seem to recall how the wonderful, beautiful commies split Poland with the Nazis and used the Pact to conquer the Baltic countries, not to mention wage a war of aggression against Finland. And if Hitler hadn't stabbed Stalin in the back, the Commies would have probably spent the entire war as his allies.
If the atomic bomb had been dropped on Germany, or been dropped by FDR (whom liberals conveniently forget hated the Japanese, just like his cousin Theodore), we wouldn't hear a word about it.
I suspect you're right -- few liberals (some, but few) would have complained about use of the A-bomb on Germany. Most are real hypocrites.