Must be a midwestern accent thing, I don’t pronounce book, “boooook” (as in what a ghost with a cough says)
Book/nook are not as in boo/goo, but they're also not the same as in buck/Zuck. This is not a Midwestern thing. I can't recall ever meeting a native US english speaker for whom these vowel sounds weren't distinct. Probably in some accents they blur together.
Rather, I think some may be rhyming Zuck with buck which does not rhyme with book.
Edit: oops, smolder said the same thing but I was reading a stale page without the reply...
Here are some pairs of words to show they don’t rhyme: