Same SSID on two different controllers: Bad idea.
1: They will try to manage the airtime and will register 'rougue' AP's broadcasting the same SSID.
2: You will have different DHCP servers on each net, and what about registration? WPA[2] or Captive? If some sort of portal is in place, you will have guests registering on two different portals, and That is gonna be a strange user experience!
Make an event SSID, or make sure the DHCP/portal is at least the same.