A SAN disk is basically just another disk on your server. It can be used for any number of reasons. Some examples:
- extending the storage of your existing server
- offer high performance space for heavy load
- offer fault tolerant storage
- offer a shared location so multiple resources can share the same content
So, you can do whatever you want with it, just like you would another local disk. Check with your system admin who added the SAN to make sure that it's assumed to be permanent storage.
However, I should say that it's common to use local disks for the installed applications and SAN storage for the content. You're not required to do so, but it will prevent services on the Ubuntu box from failing if the SAN is temporarily disconnected. If only content is stored on the SAN then the site will usually recover easier than if the entire installed application (CF) is on the SAN. Plus the installed applications usually don't take up much space compared to stored content.