Hello, I have been working on it a bit and have been able to put together something like this so far.
List Radius server status for selected zone. For each zone it will get the Authentication Protocol, all the Radius IPs (upto 4 per zone), and Auth Port if entered (1812 default) and Secret Key for each IP. I have not yet added an ability to change the username and password (just using test//testing123). It should be possible though. It also logs the data to /tmp/radiusstatus.log
Screen shot for Services -> Captive Portal
and the resulting Status -> Captive Portal page
(my radius server was down during the test haha) If you would like I can probably add a tab in Status for Radius Servers if you would like to keep the status of Captive Portals and the Radius Servers separate. Also from what I tried, you need to add the freeradius package. (I only added the FreeBSD one, might be better to add the pfSense one for more control.)
Let me know if you are interested and if so how you would prefer it. Also if I do end up finishing it for the bounty I would like to be able to provide the changes to everyone.