Eric Schwitzgebel has a post about professional philosophers (and ultimately ethics professors) in Nazi Germany. How many of them supported the Nazis? How many took a stand against the Nazis? How many tried to be neutral on the matter?
In his post, Schwitzgebel determines who the professional philosophers were by looking at the number of people who completed a Habilitation in philosophy. That's a sensible approach, but it should form only one of several criteria for counting professional philosophers.
To see why, note that one of the first academics to be dismissed by the Nazis was Paul Tillich. Though known chiefly as a theologian, Tillich had a doctorate in philosophy (but no Habilitation) and periodically taught in philosophy departments. At the time of his dismissal, he was a philosophy professor at the University of Frankfurt.
Another German professional philosopher in the 1930's who lacked the Habilitation was Karl Jaspers, who was teaching philosophy at Heidelberg in 1937 when he was forced into retirement by the Nazis (because his wife was Jewish). Jaspers' training was in medicine. I don't think he even had a philosophy degree, let alone the Habilitation.
Finally, there is Kurt Huber, who was part of the White Rose resistance group and was executed by the Nazis in 1943.
Huber's higher degrees were in musicology and psychology, but (according to the above site) Huber, a Leibniz scholar, started teaching philosophy at Munich in 1926. I think it was in that capacity that he met and influenced the younger members of the White Rose group (esp. Sophie Scholl). Moreover, Huber actually joined the Nazis in 1940, apparently due to his opposition to communism, before becoming a martyr in the White Rose resistance.