Was Gone With The Wind racist?
Yes, but as the Civil Rights movement was in its infancy, the makers can perhaps be forgiven for going with stereotypical characters - as all cinema directors did in those days. This was the time when the good cowboy wore a white hat, and the bad guy was usually chosen because the actor's eyes were close together, or he had a particularly heavy beard growth. It was of its time.
Now, people are more enlightened, and to look at the film in context is to see it as a work of fiction - it is not a documentary, nor is it trying or pretending so to be.
But the idea of a themed ball like this is not a good one, simply because it does throw up the argument about slavery and opression - and there are plenty of non-specific themes, such as the replacement they have chosen, which will not cause any offence to non-white students.