I've lived in Tennessee all my life, and it's definitely real...regardless of skin color or any other differences. There are many people who are flat out as friendly and helpful as Dolly Parton, who is loved very much by most Tennesseeans for being such a sweetheart.
It's not universal, of course...there are certainly rude southern people, but they are generally not looked kindly upon.
Also, there are the type who are very cordial face-to-face, but will share every detail about you to others through gossip. The "well bless their heart" types.
Then, there are the types who truly are racist and LGBT-hating assholes who seemingly trust and worship Donald Trump over Jesus Christ; let alone follow the teachings of Christ from the Bible. "Love they neighbor as theyself"
and "Love your enemies and pray for those who persecute you"
are the furthest things from their hearts.
Generally, though...southern people are mostly kind and cordial in public. Just don't expect it from everyone