Are you sure the installations aren't faulty?
We have an ePO environment and we've seen something similar with Workstations showing in the "Workstations without AV report" but when you check, they do have VSE installed and no problems with the McAfee agent, so they are all checking in with ePO regularly.
BUT.... on closer inspection, the Workstations had a load of McLogEvent errors in the Application log in eventvwr. Also, when you look at the workstation in ePO, have a look at the Products tab. Do you have a valid Dat version? Our problem PC's were not showing a Dat file at all in here.
Remove and reinstall VSE if you have the symptons above