Overall, yes, it is acceptable for blacks to call one another the n-word (whatever form). I don't think n*gger is used much though (at least in a serious manner). All I hear is 'n*gga' in a friendly/casual manner.
I only find it acceptable, regardless of being black or not, if it's not used in a serious manner. I pretty much just say negro when I'm joking around with my black friends but I never say it to anyone if I don't know they're* comfortable with it. If someone that's not black wants to use it with someone, make sure they're ok with it. Otherwise there should be no problem
it should only be brought to attention when someone is using it as a degrading term.