Replace this defcustom in your hypb.el file and reset it to default to grep rather than zgrep unless the BSD version is available.
(defcustom hypb:rgrep-command
;; Only the FreeBSD version of zgrep supports all of the grep
;; options that Hyperbole needs: -r, --include, and --exclude
(format "%sgrep -insIHr" (if (and (executable-find "zgrep")
(string-match-p "bsd" (shell-command-to-string "zgrep --version | head -1")))
"z" ""))
"*Grep command string and initial arguments to send to `hypb:rgrep' command.
It must end with a space."
:type 'string
:group 'hyperbole-commands)