Hi Gale,
If the reunion is not your "cup of tea", can't you learn more about your great-great grandfather by other ways other than attending the reunion? Does the family have any knowledge of the African-American side of their family? If they are aware, have extended the invitation to you and your family, and you have the desire to attend, then by all means do so if you are comfortable.

My mother's great-grandmother was fathered by a white local farmer of a "prominent" family in the community. I have been able to communicate with a descendant of that family and have gained some more knowledge about this man...enough "basic data" that suits my low curiosity and then moved on to my other ancestors that greatly interests me much more than this man. I sound somewhat "negative" towards this man for various reasons, which I may discuss later.