The Antivirus Client does require an Agent to be installed. What you can do is install a minimal agent configuration on the core. Just install the basic agent components, and then run an "Install/Update LANDesk Antivirus" task from Security and Patch Manager.
So configure your agent and ONLY check "Software Distribution" in the component list and install the to the core.
Then click the down arrow on the second icon in Security and Patch Manager and select "Install/Update" LANDesk Antivirus.
This should work great for you.
I am running AV on my 8.8 core
I installed the Default Server Configuration (scaled back) and then ran "C:\Program Files\LANDesk\LDClient\vulscan.exe" /InstallAV
Works very well
We have also put the bare minimal agent with AV on our core and it works quite well. The only complaint is there is no scanning timeout setting by file(example: Skip file if it takes longer than 30 seconds to scan). So if there is a large amount of files, many large files, or lots of files in use manual scanning can take a long time to complete.