I have never heard that Max Baer was not Jewish.
That story you related ("Yom Kippur...I'll fight him next") is emblematic of Mr. Baer's sense of humor. That story is probably true, but it doesn't reveal that Baer was not Jewish, it reveals a bit about Baer's personality - nothing serious, life is a ball, make a joke every chance I get.
Roxy, watch one of Baer's fights -- on his fighting trunks Baer wore the biggest Star of David you will ever see. You explain to me why that was there. Also, his fight against Schmeling was seen as the Jew vs. the Nazi.
Maybe Max might have been half-Jewish (I don't know), but Mr. Max Baer was a hell of a lot more Jewish than the Pope (that I'm certain of).