Interesting... so the general conclusion would be that when writing songs, you're basically 'allowed' to misuse the language in order for your song to sound better.
Specifically the ones in which rapping takes place. So basically, a rap song wouldn't sound cool unless you write it the exact same way as those ghetto people would, right? Can't get no satisfaction from proper English rapping action...
Can-not get no ... ---> means you can. Nice going John.

Those particular errors occur in my language a lot too actually.
But anyways, I always believed that when you're writing a poem, and you end up having to make changes to the grammar in order to make the poem flow better, then you're not doing it right. But I guess rap music is an exception then.