But that is not what the author wrote. He specifically said “only martyrs”...
I tend to think there were others such as Seventh Day Adventists that resisted in large enough numbers to be identified as a group.
However, other than JWs, what other sizeable group of people can be pointed to as having had a choice to remain "free" by bowing down and worshiping Hitler, or refusing and being sent to concentrations camps that chose the camps?