Hi Ryan,
From the Consolidated Platform Configuration Guide, Cisco IOS XE Release
3.3SE (Cisco WLC 5700 Series) I found this:
"On the guest controller WLAN, which can be Cisco 5500 Series WLC, Cisco WiSM2, or Cisco 5700 Series
WLC, configure the IP address of the mobility anchor as its own IP address."
My bet is that it would work, but wouldn't be supported; much like it used to not be supported in the conventional CUWN deployment with 5508 Foreigns pre-7.4.
I have a co-worker going to Live next week who is going to corner someone from TAC or the BU to get a definitive answer, because I'm looking to do a similar thing for a customer.