> (put 'diff-hunk-next :advertised-binding [tab])
> (put 'diff-hunk-prev :advertised-binding [(shift tab)])

The above, I've put in a patch for emacs-mac port, see below.

The development master as of now has

— quote

(easy-mmode-defmap diff-mode-shared-map
  '(("n" . diff-hunk-next)
    ("N" . diff-file-next)
    ("p" . diff-hunk-prev)
    ("P" . diff-file-prev)
    ("\t" . diff-hunk-next)
    ([backtab] . diff-hunk-prev)

— quote ends