At no point does he make a case that it reveals anything despicable about Ed Wood. Is there some evidence to the contrary? Would we find it in his other movies? I did a little search on "Ed Wood + minstrel scene". The first result is a Youtube video of it. No other pertinent results.
The theater that's robbed has a vaudeville component, I believe. These were still around in the 40s and 50s in a few places.
"Amateur minstrel shows continued to be performed in the 1960s and high schools, fraternities and local theater groups would usually perform the shows in blackface. The amateur minstrel shows in blackface finally died out in the US in the late 1960s as African Americans asserted more political power, but even today minstrel shows are still used as a theme for amateur productions."