Yes, you can configure in this way that your FlexConnect AP group authenticate from any backup server, these servers can be used when the FlexConnect access point is in of these two modes: standalone or connected.
And yes, it will over-ride the global config whatever Radius servers we define under FlexConnect groups.
You have to make group of those APs whom you want to authenticate from primary radius server.
Hi Did it work for you...? I have created a flexconnect Group and put my ap in it and configure local radius server which is a ISE PSN node locally available in Branch. But still authentication goes to centralized ISE PSN. I am unable to get it working.