The RADIUS connectivity used for dot1x authentication can be reachable through:
GRT
VPRN
R-VPLS (VPRN, IES)
For R-VPLS, the port terminating the dot1x is a VPLS/EVPN SAP, but the RADIUS server is reachable through the same R-VPLS L3 Service, that is the VPRN or IES that the R-VPLS is connected to.