It is possible to run two Antivirus programs on the MDaemon machine. An Antivirus program that runs in the background and checks all files - not just emails - would not be a bad idea!
To ensure that there are no compatibility problems or clashing between MDaemon Antivirus and the other antivirus solution, exclude the entire MDaemon directory structure from scanning and monitoring.
This is also required in general even if MDaemon Antivirus is not active.
There will be unexpected results if a non-MDaemon AntiVirus solution locks a file that MDaemon is using.