Haven't used it yet, but here is a Q&A that might help:
Q. Is IPv6 supported on the Cisco Wireless LAN Controllers (WLCs) and Lightweight Access Points (LAPs)?
A. Currently, the 4400 and 4100 series controllers only support IPv6 client passthrough. Native IPv6 support is not supported.
In order to enable IPv6 on the WLC, check the IPv6 Enable check box on the WLAN SSID configuration under the WLAN > Edit page.
Also, Ethernet Multicast Mode (EMM) is required to support IPv6. If you disable EMM, client devices that use IPv6 lose connectivity. In order to enable EMM, go to the Controller > General page and from the Ethernet Multicast Mode drop down menu, choose Unicast or Multicast. This enables multicast either in Unicast mode or Multicast mode. When multicast is enabled as multicast unicast, packets are replicated for each AP. This can be processor intensive, so use it with caution. Multicast enabled as multicast multicast uses the user assigned multicast address to do a more traditional multicast out to the access points (APs).
Note: IPv6 is not supported on the 2006 controllers.
Also, there is Cisco bug ID CSCsg78176, which prevents using IPv6 passthough when the AAA Overrride feature is used