Whatever the Russian Government said or didn't say, or what it told its own people, the Russian Convoys were an essential lifeline to a beleaguered country. It's all very well to say that a Red Army victory was inevitable over the Wehrmacht, but it takes more than overwhelming manpower to get there. The convoys bought the Soviets time to get their own act together, having lost most of their aircraft and tanks in the initial blitzkrieg.
If your father in law wanted the Nazi regime defeated, then his part in the Arctic War was a vital component in that, no matter how he was treated by our Russian allies.