Is there a way to hide custom fields from a volunteer with Group Leader access?
Yes, it is possible to hide a custom field from a Group Leader so that it is only visible to Administrators. In order to do this, simply change the custom fields requirement field to "Yes - Hidden (Admin Only)." By setting the requirement value to this, you will limit the access (both viewing and editing privileges) to administrators.
If you would like a Group Leader to have some control over their group, but not full access to all of the group volunteers' profile information, you can assign them as the primary or alternate contact person for a group (in the Group Management section), but leave their CERVIS access level set to "Volunteer". This will allow them to add members to their group and register for events on behalf of members of their group, but will not allow for full access to personal information.