Well, let's tear it down
RADIUS runs locally on every AP = unique RADIUS user pool per AP roaming presumes presence of known authentication = not possible due different RADIUS databases
If we talk about scenario where the RADIUS user pool is shared (or static) then "roaming" obviously works, but
this is not seamless roaming at all.
From RADIUS perspective the MAC address associated with the user account is not known - with RADIUS onboard-self every AP runs own database of account / MAC combinations with accounting on its own. When you roam, you go for re-association based on WNMP but then you hit the edge of EAP authentication and RADIUS server will start to send challenges instead of recognizing the client MAC.
In my opinion this is unnecessary mess you can easily avoid by mapping the RADIUS to either RFDM or centralized controller. Moreover, if Vendran wants to use Captive portal, that would bring extra layer of complexity.
I'd definitely go for elegant option A and rather use multiple (per-site) user group / user pool.
Regards,
Ondrej