How to remove 'Volunteers' menu option where it's not appropriate?
Not entirely sure, yet if menu comes from CiviVolunteer 2.2.2 extension, perhaps an extra permission check should be added here: 
https://github.com/civicrm/org.civicrm.volunteer/blob/59534288f37c96202434c57adc73d2fa5dc7ba55/volunteer.php#L46