I don't question your interpretation of the use of 'Heman' as an African-American name. I was swelling out its history as a proper name, since using a surname as a first name once was not uncommon in the South.
Your project on names is interesting. As a student, for awhile I had a part-time job with the Texas State government checking census, poll tax (fee $5.00- I still have my receipt), and other records. I remember some of the names, one of which was Lemon Meringue, but I don't remember the racial designation. Those records, if still in existence, would be a gold mine of names, since race was indicated.