"Did the defenders of Fort Wagner consider it to be an insult to bury a white officer with his black men at the time they did it?"
Based on the culture of the time, I would think that they did not have much respect for the black troops and becuase of those feelings, they did not have any respect to the white men commnading them. So they just dug the hole and placed them in and covered them up as you say. I would think that there would have been a lot of hatred for the black troops and their commanders in any case. In my opinion.
FC