Seems pretty straightforward, actually:
“We need to cast someone to play a Nazi for this episode.”
“Remember that one guy we cast in Voyager? He was pretty good. Let’s just get him back.”
Both series had the same primary casting directors:
https://m.imdb.com/title/tt0244365/fullcredits/casting_director?ref_=m_ttfc_8
https://m.imdb.com/title/tt0112178/fullcredits/casting_director?ref_=m_ttfc_8
To be fair, if you’re a character actor in Hollywood, can you really afford to be turning down parts merely because they’re typecasting you?
As long as people are making media with Nazis in it, someone’s gonna get cast to play the Nazi. Might as well cast someone who understands the role.
It doesn’t mean they believe in it, which is discussed in the very article you linked.