You could make a custom report to accomplish this. The query below should show all helpdesk users and the amount of tickets they are the current user of.
SELECT htblusers.name, count(htblticket.fromuserid) amount from htblticket right outer JOIN htblusers ON htblusers.userid = htblticket.fromuserid group by htblticket.fromuserid, htblusers.name ORDER BY count(htblticket.fromuserid)
A more advanced query (see below) will take history into account and shows the amount of tickets created/duplicated for all helpdesk users.
SELECT htblusers.name, COUNT(htblhistory.histid) FROM htblusers LEFT OUTER JOIN htblhistory ON htblhistory.userid = htblusers.userid WHERE htblhistory.typeid = 13 OR htblhistory.typeid = 31 OR htblhistory.typeid = 38 GROUP BY htblusers.name ORDER BY count(htblhistory.histid)
Note that both queries will only use users already defined as a helpdesk user, not all scanned users from Active Directory. To accomplish the latter you'll have to link tblADusers to htblusers as well using their domain and username.