There are reports it could work but CIS was never developed for and tested on Server OS. Ronny, one of the moderators, tells us the following:
I have it running on several 2003/2008(R2) 32/64 bit versions.
In general it runs fine as CAV, I have had some issues with running FW & D+ on some servers but not on all, it seems to depend on the roles/applications/tasks the servers are running.
In short: your mileage may vary and you are basically on your own.