You make good points, Jeff.
In Radio, Eddie Anderson was one of a number of black artists who, in a sense, crossed the color line successfully because the medium enabled a wider audience to absorb another culture without becoming "uncomfortable" about its own racism and bigotry. And the FCC, by the means of logs and airchecks (the main reason we still have the shows to listen to), kept Network Radio from giving, for the most part, vent to the more extreme forms of American bigotry.
In fact, it is quite remarkable, if you listen to much Radio of the time, across the spectrum, how many appeals are made for "tolerance" of all kinds. So unlike our media world today, where gasoline is cheerfully thrown onto horrendously volatile situations.
Anderson and Benny, in part because of the understood but unstated recognition of a minority partnership on Radio, appear to have been accepted with near universal affection.
In connection to our subject here, your reference to Lena Horne in CABIN IN THE SKY, reminds me that Welles in the recent past had been negotiating a professional relationship with Miss Horne, and carrying on a romantic one.
[It was a reason J. Edgar Hoover directed that an FBI file be opened on him.]
As for Charles Correll and Freeman Gosden, it is hard to fathom now, given what was the reality of race in America in the period, how popular their continuation of minstrelry in our national life. It has been noted that, during the Depression, companies often allowed those lucky enough to have jobs to take off work early in order to be home to hear "Amos n' Andy" during the dinner hour.
Largely because of the medium of Radio, Freeman and Gosden were were able to appeal to people of good will and bigots alike. They were regarded with a wide acceptance. It is said that "Amos n' Andy" had a considerable following in the black community back then. Thus are hatreds, guilt, and grief often assuaged.
Growing up in a little Northern Ohio town, I seldom saw a black person. [Not until long after did I realize that, in the late 1920's and early 1930's, the fathers of some of my schoolmates, as part of the Klan (almost as popular in a number of Midwestern States as it was in the South), had run most black people out of the area.] The only black person my age I knew personally was the only black kid in our high school. I'm sure that gathering around the radio in my family home, I did not know that "Amos n' Andy" were white minstrels.
Much bigger and of longer duration than Orson Welles, Freeman and Gosden were major stars in Radio, a medium which in the early 1930's, at least, Hollywood thought its major rival.
This may explain (but not excuse) Welles taking Freeman and Gosden into his production of State Fair. My guess, too, is that Welles, with his habit of associating himself with theatrical traditions of America's past, would have appreciated, without necessarily approving, the place of minstrelry in American Social History.
He certainly made up for his racial gaffes, at very great cost to his career, later. It might be said that the defense of minorities, the perfection of our democracy, was a driving, if not the driving force behind his most of his artistic endeavors in regard to America.