They weren't "made POW's". Admittedly, their participation wasn't voluntary. But, they and their families were kept under rather decent conditions, and were instructed to teach Soviet scientists everything they knew about rocket technology. They were never really allowed to participate in that research however, which ultimately led to lackluster results.
Then, once the Soviets had determined that they could provide no additional information, they and their families were allowed to return to Germany. That doesn't make them POW's. They weren't punished for their roles in the German war effort. They were simply treated as useful sources of information, and then let go.