What's interesting is Willy Ley who left Germany and did not like the Nazi's took an anti-ETH stance in regards to UFOs.
Rocket Pioneer Hermann Oberth embraced the ETH and Wernher von Braun according to Dr. Carol Rosin spoke of ETs.
Willy Ley had an interest in cryptozoology/zoology. Could he have been like a Donald Menzel doing classified work regarding aliens and openly spoke out against aliens like a Donald Menzel? Perhaps Willy Ley was studying the alien anatomy from from bodies recovered from crash retrievals.