Sharon, interesting your society would find "Mammy" offensive. It is found in other traditions besides the minstrel shows - I've heard it in Irish songs for instance.I'm not sure about Hoecake, but "Ho" seems to be slang for whore nowadays. Maybe that's the connection.
I've got to agree with most of the comments on Political Correctness. I dislike PC in general and particularly when it comes at the expense of something else. But it's important to know the background of a song so it can be presented in context. We all need to be aware of and be able to see things from other points of view. That is the foundation for true tolerance and sensitivity. I would put the responsibility on the performer to present a possibly offensive song in a sensitive way by giving whatever information is necessary for the audience to see the song from a point of view that will nullify its offensiveness.