Ask them to define exactly the concept of "anti-virus". What kind of threats are they worried about?
If they cannot answer (maybe because they really have no idea what they are talking about and are just filling a check-list), ask them a list of approved anti-virus programs.
If the requirement is just:
You shall have an AV program installed, period.
they probably have no idea what they are talking about. Just ask them what they expect you to do exactly.
If the requirement is:
You should regularly check all installed programs (binaries and scripts) for new programs, altered files, or any other sign of pathological file content.
then it means you may not need the proverbial "AV", and that a script to check the integrity of the server will be adequate, more precise, more reliable: no false positives if you know which files are modified when your server is running normally, and if you can spell out the consistency requirements of modified files.
Designing a script check the integrity, or even setting-up some existing tool so that it understand the specific of your server will necessitate additional work (AV programs are more buy-then-install-then-forget, that's probably why they are so popular). But I think that will do much more for your server security.