We evan had a nazi soldier become a Pope. But you're right, none of the allies war criminals was punished.
The German army was just German army, not specifically a "Nazi army" even though the country was lead by Nazis and even though modern click-baiting headlines equate the two.
As far as I know, Ratzinger had nothing to do with National Socialism beyond what was compulsory and unavoidable under pain of death in Nazi Germany (i.e. being drafted).