1.) Whether "nig" is a back-formation from the well-known racist term for American Black people, or branches off from that other pejorative, “niggardly,” what’s plain is that the mere utterance of the word so traumatizes many of us that—-unlike any other word I know—-even the linguists of EL&U have great difficulty extricating themselves sufficiently from a past we find deeply shameful to appreciate the extraordinary evolution that this word has undergone.
2.) As correctly stated by the OP/Answerer/Editor(?), “Niggers Gonna Nig,” is a snowclone of “Haters Gonna Hate.” In order to snowclone the original the initial 2-syllable word “Haters” became “Niggas,” and the final single-syllable word, “Hate” became “Nig.” While some may claim that “nig” is a truncation of “nigger,” it has no currency in the US in that sense. “Nig,” as short for “nigger” is only used by closeted racists fearful of being overheard and thus outed, especially when scary Black people are within hearing range. Whereas, proud racists relish fully pronouncing the N-word and loudly proclaiming their vaunted ignorance a virtue before all.
3.) Additionally, though the text at the bottom of the picture in question reads, “Niggers Gonna Nig,” if you hover on that pic you’ll notice that the photo is actually tagged, “Niggas,” and not Niggers. This is not a quibbling distinction, for the two words have opposite meanings today. “Niggers” still means what everyone knows that it means. But, in a potent act of cultural hacking with deep political implications, while Massa slumbered serenely dreaming of empire, the black youth of America crept into his white house, stole the Massa’s forked-tongue, and liberated themselves from the hateful label that had shackled and diminished them for the last 500 years.
4.) Initially this hijacked term was reserved for Blacks. But words that truly resonate (for good or ill) always gain wide currency, and so over time the term came to be applied to any non-Caucasian peoples. As employed by the most progressive of today’s youth, however, “Nigga” or “Niggas,” is a term without racial bearing in many (not all) situations, applied to any person who is a victim of prejudice similar to that suffered by Blacks; to any person who is economically, politically, or socially disenfranchised. In other words, in the most liberal sense, “nigga” now means “true or real human; just plain folk; comrade; and even more which I don’t care to document right now. Wikipedia check-it-out gets pretty close but doesn’t go quite far enough.
5.) The graphic media that gave rise to this controversy was created by Sean C., an American Black from NYC with the brand, "Satisfies69". Sean C. acts as an agent provocateur who specializes in multimedia “shock-art” that is deliberately as iconoclastic as possible—-mocking all aspects of modern culture’s double-standards, violating all its taboos, and holding the funhouse mirror (as it were) up to society’s shadow-face. While at first blush Satisfies69’s work may strike one as the First Amendment’s worst nightmare, and merely vulgar or pornographic (and much of it is!), I find it highly doubtful the work is intended to be racist. Much of his work (I believe) is also socially and politically relevant and meant to deflate our pretensions and exorcize our "badder" devils.
6.) Contrary to the commentary, “Renig,” is pronounced ‘re-nig’ and not ‘re-neyg,’ by native AmE speakers from the working and under classes—-White and Black—-without self-consciousness or irony. As was mentioned, renig is a term used in the card game, Spades—-how ironic is that—-a favored past-time of the millions of White and Black inmates warehoused in the gulags of the United States, and again, is without etymological relation to that hateful ol' racial mojo.