This raises all sorts of questions, but I'm interested in exactly what "style and accent of another culture" you are talking about here? You seem to be assuming that there is such a thing as Hip Hop culture, if there is such a thing then can you explain what it is made up of, and what particular kind of language needs to be spoken to be considered a part of this culture?
And you also seem to be implying that Hip Hop culture is exclusively black, and that in order to truly be a part of that culture (as opposed to being an outsider or voyeur) you should be black? That in some way, by not being born in to something, you can never truly belong?
You could argue that by not being born in the US - and let us say (for example) New York or Los Angeles - you are not part of the 'culture' - and that even by being black you are still excluded and not quite 'keeping it real'.
Have you not considered the fact that many of the stylistic affectations that pass for 'keeping it real' are used by black Hip Hop artists (and those involved more generally) too? That their vocal 'keeping it real' is just as much an affectation as Tim's?
BB