Many, if not most, “blacks” in the South are members of the American Methodist Episcopal Church, link to which is contained in the post above by Guinastasia, or the similarly named African Methodist Episcopal Zion Church. Those churches are literally EVERYWHERE, since they often have smaller numbers per church. You cannot drive around the South without seeing signs for them all over the place.
About 6% of the members of the Southern Baptist Convention identify as “black”, according to the Pew Research Center. Since there are about 16M Southern Baptists, that puts the number of “black” SBC members at just under 1M. The A.M.E. Zion Church claims 1.6M members; the A.M.E. Church claims around 3M members. How many of those combined numbers are in the South I cannot say (there are a few other, smaller denominations which are roughly equivalent to those two). But clearly, one cannot say about “blacks” in the South that they are almost all Baptist.
As to the general question, if you drive around in the South, you will find several churches well-represented. Clearly, there are a lot of Baptists. But there are a lot of Presbyterians (the South was originally well-settled, especially in the uplands, by Scots), Methodists, and, of course, Episcopalians, the old, “established” church of England. In addition, there are a growing number of non-denominational churches (an example around Charlotte is Elevation Church). Plus, there are the old standbys like Church of Christ, Assembly of God, etc. A large number of Southerners are certainly “evangelical”, but you can be evangelical and not be Baptist.