If you're a black GI from Baltimore, I expect that calling fellow Black GIs from Baltimore "nigger" would probably be the natural thing to do, in much the same way that white boys from Essex call each other "mate".
If you're a white middle class boy from the home counties, such as I am, it would sound rather odd, regardless of how friendly you were with those black GIs.
Talking of Baltimore, you don't ever see any of the white faces in The Wire use the word nigger, except one street dealer who is the archetypal "wigga" and very much a figure of ridicule. For that matter, nor do any of the black people in positions of authority in the show (cops, politicians, teachers, religious leaders) use the word, even though it is a word that is uttered frequently.
Again, it all comes down to context.
d.