Hi Zac,
You can try creating a sql based filter by joining the dbo.vuser and dbo.Inv_AeX_AC_Primary_User. The only thing not sure if user is the same as name in the two tables... i.e.
select a1._ResourceGuid, i.name from (select name, domain from dbo.vuser where department like 'departmentname') aduser
JOIN dbo.Inv_AeX_AC_Primary_User a1 on aduser.name = a1.[user]
JOIN dbo.vitem i on a1._ResourceGuid = i.guid
WHERE a1.[Month] = datename(month,dateadd(mm,0,getdate()))