To be honest, it's should not be any different installing VirusScan on a server with ePO installed than without.
Where did you see it documented that it's required and that there were restrictions ?
Just asking so I can take a look
It's in the EPO 4.5 Install Guide, page 6, under the Security software Section
Install and/or update the anti-virus software on the ePolicy Orchestrator server and scan
CAUTION: If running VirusScan Enterprise 8.5i or 8.7i on the system where you are installing
ePolicy Orchestrator, you must ensure that the VSE Access Protection rules are disabled
during the installation process, or the installation fails.
That's just common sense, we don't actually enforce it through the ePO installation.
In other words ePO won't be blocked from installing if VSE is not present first but if you are installing a server application that is about to control your entire AV deployment you'd probably want to be sure it was clean first
The access protection rules note is a good point though.