Unless I'm mistaken, SmartArray P4xx RAID Controllers allow adding disks to an existing RAID set using the ACU (Array Configuration Utility) if BBWC/FBWC is present.
After expanding the RAID set as well as the logical volume on this RAID set, you need to grow the VMFS datastore from an ESXi host. Depending on the controller, the datastore may be presented as remote storage, and since it's not the installation volume which you are trying to expand, it may even work to grow the datastore from the vSphere Client. If this doesn't work you'll have to resize it from the command line (see http://kb.vmware.com/kb/2002461)
André