No, but with different code, if the ap moves to the other WLC, that ap will have to upgrade its code and you will have downtime. As long as you have created the dynamic interfaces (different ip but on the same subnet) and created the same ssid and map that to the same dynamic interface, then everything should work.
You also have to verify the switchport configuration and make sure that the vlans are allowed on the trunk port of the new WLC.
Well since the ap's only know of the existing WLC, the only way they will join, is if you remove the existing wlc and let the ap's find the new wlc. When you configure the mobility group, that info is pushed to the ap, so that it knows of the new wlc. This way you can set the primary ap to the new one and the second wlc to the existing wlc.... make sure ap fallback is enabled so that the ap will try to join the new wlc. If you still have issues, I would console into the ap and capture the log when you faile the existing wlc.