Cisco :: 5508 - Failover For Multiple WLCs And Mobility Groups

We are in a warehouse type setting and have data centers on each side of warehouse with 5508 WLC's in each data center. Each side is on its own subnet with routing in between and a different set of SSID's for each set of WLC’s. Are goal is to have the ability to failover in the event that if one data center goes down AP’s will move to the controllers in the other DC and the clients will still be able to operate.
 
Our thought was to implement mobility groups between the controllers. While I saw documentation on setting this up when the controllers are on the same vlan, I didnt see any setup config when controllers are in different vlans. So I am wondering if mobility groups are even an option for what we want to accomplish. For the most part clients stay on their respected sides of the warehouse and so we are not necessarily needing roaming for clients between controllers in DC1 and DC2. But that does raise another question in that we do have a planned voice wlan that we would like to have the ability to roam between each side of the warehouse. But we have seen ip issues with this. In the past we have had both SSID's setup on each side and ran to issues with clients not renewing their IP address when moving to the controllers on the different subnets.
 
Can we setup mobility groups between controllers on different vlans/subnets? For failover purposes will mobility groups assist in our setup with 2 DC’s and different subnets/vlans? If the answer is yes we can setup mobility groups between different subnets, is there a way to setup the SSID's on all controllers and have the ability for clients to roam and renew their IP’s when moving to a different controller on a different subnet?