HI,
in a master/standby deployment. You need 3 IPs. IP master controller , IP standby controller and the same virtual IP on both controllers.
The virtual IP (VRRP) is used for provisioning the AP .
"The master controller owns the configured virtual IP address for the VRRP instance. When the master controller becomes unavailable, a backup controller steps in as the master and takes ownership of the virtual IP address. All network elements (APs and other controllers) can be configured to access the virtual IP address, thereby providing a transparent redundant solution to your network."
Look at this:
http://www.arubanetworks.com/techdocs/ArubaOS_61/ArubaOS_61_UG/VRRP.php
Best regards!