Anything under /usr/libexec is explicitly not for end users, but only for use by other programs, so I don't think a man page should be a requirement. Some of the pacemaker child daemons have man pages, but only because that was a convenient place to document cluster-wide options that affect them.

pacemakerd (in /usr/sbin) is the only daemon binary intended to be invoked by a user (though normally even that is through systemd), and it has a man page.