Can I run different versions of VCS in the same cluster?

No, absolutely not! Different versions of VCS, and even different patch levels of VCS, cannot run at the same time in the same cluster. Therefore, when you install VCS patches, you must install them on *all* nodes at the same time! The cluster will have to be partially or completely shutdown during upgrades or patching. Of course, you can shutdown VCS without shutting down your services.