It seems like we're still not detecting or doing something right with clamdscan on CentOS 7.
This thread indicates it can't be setup automatically, and sometimes even when it is started manually it fails to be detected (that might be a different issue though...maybe their network is slow and the initial download of the virus database is timing out or something).
The proper name of the service we need is firstname.lastname@example.org
Also, note specifically this comment: https://www.virtualmin.com/comment/750881#comment-750881
This one may indicate I need to do something in the package, if it's setting permissions incorrectly. I'll look into that, but I think there's also something wrong in Virtualmin itself.