The word causing so much contention here was originally Latin (Niger, etc.) but entered into European languages in the 16th C.(see OED, under Neger and Niger, as well as Negro (Spanish), nigger). I agree with Dick Greenhaus and Big Mick on this. McGrath is correct, there is no substitute for the correct name in an index.
If you check Allen et al. at the North Carolina- Hampton site, the 1874 fragment given is NOT a spiritual, but an old slave party song. It was also associated with the underground railway. The words given by McGrath belong to a spiritual that is unrelated to the song being discussed here. Several "spirituals" have been posted in the DT that are combinations or arrangements for gospel singers or white (dare I use the word?) choirs. The Black cable channel has been added here in Canada; Black stand-up comedians use the word in their routines, as stated in a post above.
Deletion of any word, to me, is censorship; the recent tendency toward sanitizing the language is the worst kind because it subtly erases the past. Dialect is also under attack; at least the Scots preserve much of their language (see the Scottish dictionary that has been posted here).