Controller Based WLANs

Q:

We have a master-local setup running on 6.4. and another master-local setup running on 6.5. Can we have one of the controller in the 6.5. setup act as a licensing server for both the 6.4. master-local setup and 6.5. master-local setup?

No, this will not work. 

In 6.4 Master-Local, Master will become default license server to the locals after enabling the centralized licensing. This can not be changed. Even configuring "license server-ip" will not take effect on Locals. Locals will be pointed to master ip and master will be pointed to configured "license server-ip". This will lead to mis configuration.