If you're intent on imagining a subtext to Night of the Living Dead a movie which never mentions zombies and features the (undead) neighbours harrass a black man who is ultimately shot dead by a sheriff’s deputy then you might also want to recall it was conceived in the aftermath of the Detroit and Newark riots and released to audiences who had just seen National Guardsmen shoot antiwar protesters to death at Kent State University.
I'm not saying that movie in particular had that subtext. Rather, the zombie trope quickly took on a life of its own in the years after Living Dead (and split into the fantasy/cursed and scifi/infected subtropes). It's hard to say why it resonated but there are definitely some interesting parallels with other cultural trends.
It's an interesting film, as an Australian who came to it later (I think I first saw it in 1992 ish) it was a while before I apprecriated a whole other perspective it had for some (early case of a film with a black lead, early use of graphic horror, lead character being killed, etc).
The thing about tropes in movies and literature is that they are often identified and become part of the legend of a work without the intent of the autor.
Whether intended by Romero or not, according to the documentary A Century of Black Cinema (and other related print works) the film had a profound impact on many African American viewers of the time .. because of the lead, because of the story, etc.
Whether it was the original plan or not, by the time the movie gets to the end credits the parallels to a lynching are incredibly explicit.
I'd like to put in a rec for https://www.imdb.com/title/tt0053454/ "The World, the Flesh and the Devil", which is an apocalypse movie with a slightly different premise: what if the only survivors of an apocalypse in apartheit 1950s America were a black man and a white woman? Contains some great shots of deserted New York and some very intense performances.
It's kind of interesting to read about contemporary reactions to Night of the Living Dead, which included "it's obviously a commentary on the Vietnam War" and "a critique of American capitalism". The closest anyone got to racial issues was the observation that at the end, the (black) main character is killed by a (white) posse led by a sheriff -- which seemed to some people to be an obvious commentary on the Civil Rights Movement and the recent assassinations of Martin Luther King, Jr., and Malcom X.
The modern (21st C) vogue for zombie apocalypse movies pretty clearly stems from two sources: Japanese video games in the 1990s; and a pair of British films in the early 2000s: Resident Evil (based on one of the aforementioned Japanese video games) and 28 Days Later. (It's a bit hard to argue that both the Japanese and the British were acting out some deep-seated fear of a black slave uprising.)
both of which have been cited by Romero as events he watched while writing the film. I'm guessing that perhaps you skimmed over those and mentally bundled them in with the Kent State shootings as "obviously Vietnam war"?
https://www.criterion.com/current/posts/5390-night-of-the-li...
Shuffling drug addicts is one influence I have no recollection of Romero ever mentioning.