Good News:
The most recent firmware update for the Reach RS3 (33 Beta 3) provides seamless radio connection between the Topcon Hiper VR base station and the Emlid Reach RS3 rover when Emlid’s UHF antenna is used. Tested with TrimTalk protocol, RTCM MSM3 correction format at 458.xxxMHz.
I assume it will work well as a rover with any other 3rd party bases when the above settings are used.