I'm inclined to believe Wikipedia and other online sources regarding Jolson.

I don't think there's necessarily a corelation between performing in blackface and human rights activism. Please read the paragraph here on blackface, second section down. This is from Jolson: A Biography by John Kenrick (Copyright 2003). It puts the use of blackface into the context of the times. Does that explanation sound credible to you?

Besides Wikipedia, there are other places that talk about Jolson's anti-racism, such as this: "Actually Al Jolson was noted for his anti-racism back in a time when 15% of the American voters were members of the KKK. He helped introduce black music that he was influenced by to a mainstream white audience and fought to allow black musicians to be given the chance to perform. It's noted also that he was the only white man that was ever admitted to an all black club in Harlem back then too."

"Al Jolson was a civil rights activist who threatened to “punch” restaurant owners if blacks were not seated and served equally to whites. He purposely used blackface to bring black music to white audiences, to foster understanding between races; and was responsible for the first black performers allowed on Broadway. These facts should not be omitted from the discussion. It unfair that Jolson’s contributions to African American rights are automatically considered offensive when they are depicted. Instead of hiding and burying these facts, we should widen the discussion to include how this era in history served to strengthen race relations and move us forward as a society."

I could be wrong. It could all be revisionism. I'd be interested in anything you find that contradicts this.