Welcome to the dahlia forum, UncleWill! I have family in SW Virginia who grow a lot of dahlias. I'm not sure what zone that is but I've been down there on some brutally hot days. I have no idea whether your area would get hotter and more humid than their's in a more mountainous area. We get enough heat in NE Ohio to make the dahlias wilt terribly during the day but they have always perked up by morning. We also get some mildew during humid periods. There are/were at least a couple dahlia suppliers in NC, not sure what part. That would be a great place to ask about heat resistant varieties. Dahlias are certainly worth a try.
As Gary said, dahlias definitely need to be supported, especially the larger dinner plate types. We often get high winds from Lake Erie in the spring and fall. I start staking mine when they're 12-18" tall.
