I personally do not understand what you are asking for here.
MWG can use RADIUS authentication for GUI and for user auth (not many people use it though).
I don't understand what you are saying about "logs of configuration & policy changes on RADIUS Server??".
My be you are you need something like SIEM not MWG to view the changes in log.
BTW, MWG in not going to do any changes in other appliances same as SIEM too.
But if you want to review the logs, track the threats or unexpected changes and etc... in Appliances on one point, then you have to use SIEM product.
I agree with MBM on this one, it sounds like your asking about a log server of some sorts. You can push your MWG audit logs to a log server.
MWG has a unique audit log format so it's a bit tough to parse..
RAIDUS is for authentication, it has nothing to do with logging.