This would have gone straight over the head of all the children watching 'Dumbo' when it was first released, but it would have landed with the adults, and that makes is a strange thing to do. Jim Crow's name is a reference to some laws from an era America would rather forget.
The so-called 'Jim Crow laws' were used to enact racial segregation in education, transport, and various other public places. Quite why Disney thought that would make a suitable basis for a character is unclear.