Taking the position that it is acceptable to use slave labour to save your life from the authoritarians that you volunteered to work for during war is only a hop, skip and a jump away from saying that it is acceptable to use slave labour to save your life from the people attacking you during war.
This is but one of the moral hazards of the kinds of activities that von Braun wilfully participating in.
In a different world where the United States and Britain more closely followed the moral ideals that they profess as cornerstones of their nations von Braun and other Nazis would have been tried and executed for their actions. Or in the very least coerced to work for them in sparse cell in a remote location for the rest of his days.
The rehabilitation of von Braun and his admittance into American society is a great stain on the ethos of the nation.
He was also arrested by the Gestapo and threatened with execution if he was not more diligent in his efforts to develop the V2 missile.
I don't think it is implausible that he was less than enthusiastic about nazism. And once he was in the rocket program, there was no way out for him.