The Reich, I think, didn’t care if you took a different faith. They believed Jewishness was a genetic disease that had to be eradicated by killing all carriers of the gene.
Thanks for your answer, SJackson. I guess I'll have to look into this further when I get a chance, because it's complicated. For instance, consider that many thousands, maybe hundreds of thousands of people of Jewish ancestry were killed in WWII, even though they were baptized Christians, because to the Nazis they were racially Jews. It was a race thing, a race-euthanasia.
This is how a Catholic saint, Edith Stein, was killed, even though she was a Carmelite nun: she and her sister Rosa were arrested in the convent which was their home, put on a train to Auschwitz, and gassed the day they arrived.
At the time of her canonization as St. Benedicta, just a few years ago, there was a spate of controversy because the question was tossed about, "But was she killed as a Jew or as a Catholic? And, if as a Jew, can the Catholic Church claim her as a martyr?"
It's fairly clear from the record that Sr. Benedicta/Edith would have said "Yes, both.' But sometimes the person's own self-understanding is not taken as the last word.