Heman is an alteration of the name Hemann or Hemmann, which is Germanic. The name is not uncommon. Heman as such appears on 310 immigration records (which, of course, are incomplete; there probably were more before a system was set up to handle immigrants).

Your name applications 'uncle,' etc. apply to the large area where the white population was Protestant-dominated. A smaller area, parts of Mississippi, most of Louisiana, and southeast Texas had large Catholic populations, the white Creole population with many French, but some Spanish, entrepreneurs and land holders. Slaves would often be referred to by a Christian saint's name, e. g. Aurore and Marie, but use of Tutu and similar familiar names were used to close family of elderly servants, as they are in many areas of the world. Greater tolerance of African customs and habits, as long as the slaves paid lip service to Christianity, meant that these customs lasted longer in Creole areas than they did in more protestant areas, where survivals were not tolerated.

The development of a mixed Creole population, ranging from slave to freeman, with its subclasses, also had a strong effect on racial interaction, which is difficult to understand today.
(Don't ask me to define the meaning of Creole in Louisiana, it means different things to different subgroups. I have used it in two senses here).
A few of the songs and dances of the slave population in Creole areas were preserved by Lafcadio Hearn, Henry Krebiel and George Cable, who knew and corresponded with each other. I will post a few of these secular songs later today.