Joseph Scholmer was a German Communist and anti-Nazi activist who was eventually imprisoned by the Nazis. After the war, while living in East Germany, he was arrested on a trumped-up charge and wound up in Vorkuta, a Gulag camp in the arctic and later recounted his experience in the book Vorkuta (New York: Holt, 1955). He wrote that had the Nazis announced that they were coming to liberate the Soviet Union, four million Soviet citizens would have joined them and Hitler would have won the war.
General Vlasov offered to fight for the Nazis, but Hitler was leery of having a Russian Army fighting on his side, because he figured eventually they would turn on the Germans, which frankly, he probably was right about.