You can check if group member is group moderator. Working example of this hook is Group Moderators. true means is moderator while false means is not a moderator.

https://www.opensource-socialnetwork.org/component/view/5457/group-moderators

<?php
function group_moderators_init() {
		if(ossn_isLoggedin()) {
				ossn_add_hook('group', 'is:moderator', 'group_moderator_hook');
		}
}
function group_moderator_hook($hook, $type, $return, $params) {
		//$params['user_guid'] contain user guid
		//$params['group'] contain OssnGroup instance
		return false; //means not a moderator 'true' means yes
		
}
ossn_register_callback('ossn', 'init', 'group_moderators_init');