Just chiming in right quick:
“aa” as Charlamagne Tha God has said is a term of endearment while “er” is hardly used in the same way as it is usually used in a demoralizing way. There is a clear differences in the way both is used.
That’s all I have to say on the matter.
What about white people using the former?
Don’t mind it at all and I’ve heard the latter said by my white coworkers so many times it doesn’t phase me anymore though I would prefer that it isn’t used around me. Unless it’s being used in a joke of course. I can’t trust anyone who can’t take a good race joke.