Something that neither of you have mentioned. These three men were invited and included in being in the picture by the White Officers. Otherwise they would not have been in the picture.

They also carried authority.

By that from what I can see in the picture, I would bet you that if any one of these aides went to any of the company Officers in this unit and said Colonel "so-and-so" said go do this, or Major "what's-his-name" said go do that, I don't think that those junior officers would go complaining to the Colonel or Major about sending their "darkies" to give them orders.