Richard
Like you I have been investigating and have been in touch with 2 Border teams.
I am concerned that I do not support anything that is rascist and therefore feel that I need to investigate further, to the point where it can be proven that blacking up in the Border Morris case was to do with disguise and not for any other reason.
Having spoken to these 2 teams, it would seem that they are trying to keep the traditon going that their forefathers did. As far as they are concerned the issue of blacking up is related to disguise and nothing else. They only dance in their local villages. Make of that what you will.
I will keep on coming back, as I find out more, whether it supports the disguise or other reasons.

Looking at the video of Motley Morris, I find it difficult to believe that they are trying to take off black people. My imagination, does not stretch that far.