No, I have not read Ariela Gross's book. I don't write much about Jim Crow since I concentrate on people born during the colonial period, but we should keep in mind that the history of many of these communities: the Melungeons, Lumbees, Nanticoke and Moors of Delaware, etc., start with the Jim Crow Period in response to laws requring them to go to school with the former slaves. (They had no connection to slavery and thus were culturally white, so it is not surprising that they would minimize their African ancestry to protect their lives and property). Even the anthropologists who studied them described groups with no proven Indian ancestry as "Indian, white and possibly some Negro." So, we need to take the thinking of the time into consideration.
Paul