If a CA CSM database file system is found not mounted while I am running CA CSM, does that mean that it is no longer being used so I would be able to delete it?
This depends. Check under Settings tab, System settings, Mount Point Management and if automount is checked off/enabled you should not have unmounted file systems.
If automount is not enabled then you will have unmounted file systems and CA CSM will try to mount them on demand when they are needed.
If automount is enabled and you found a file system unmounted I would recommend checking the MSMLOG for mount failure before deleting it, I would also open a case with CA CSM support to have it researched.