I haven't seen any evidence Irving Berlin was racist, although I don't doubt that he may have engaged in the racist speech that was the usual practice of the time. This excerpt (click) from Irving Berlin's American Musical Theater (by Jeffrey Magee, 2012) makes it seem that Irving Berlin was almost heroic in defending the Afro-American cast members of This Is the Army in 1942. But yeah, I suppose he must have used racist speech - everybody did.

-Joe-