Generally, a reboot is not needed after virus definitions are updated. If you have to run something like the SuperDAT to fix issues with some of the components, a reboot may be required.
We cannot afford the EPO license and are behind a firewall. The most reliable was we've found to update McAfee is to d/l the current SuperDAT centrally and then run it on each machine. This tends to require a reboot on many machines - is there a way to update without requiring a reboot?
Except for Consumer products - a SuperDAT based DAT update should not require a reboot.
If the newer dat version fails to get refreshed - you could disable/enable On-Access protection to refresh the dat version.