I think rapping and singing are slightly different talents but there are some great voices within rap. Either way you still need to understand melody, rhythm and harmony. Rap and its antecedents have been around for longer than one might think.

Here is a rapper from 1969 working with Jimi Hendrix and Buddy Miles



This is Joe Tex doing Papa was Too ( a version of Tramp) notice that the cadence is somewhat close to modern day rap although this is also from the late sixties -1968 I believe.



"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.