Yes they can in fact say this. You do realize english is not the only language that exists or ever existed right ? Or that northern american culture is not hegemonic (yet) ?
Niger/nigra/nigrum is a latin word that simply means black or dark without all the prejudice attached to it in english, and believe it or not, variations of that root word still exist in a shitload of european languages and dialects to signify the exact same thing : a color.
To claim as you do that the denigrative usage of the word is the only understanding some farmer from the depths of the Urals should have is frankly preposterous.
What’s preposterous is the number of people who get upset, make excuses, and try and throw it back when I call out racism. Before I paste what I said in another comment, I’d like to point out that I specifically said that some non native English speakers may be ignorant of the history of the n word. Anyway:
While I understand the similarity with the latin languages, as it shares that origin, it is its own word. The actual word is being used, not words that sound alike, as it was exported by colonial powers.