Update:
I'm now running USBIP to port the UAT SDR's USB traffic from the second RPi to the primary with dump978-fa running on the primary.
My /etc/rbfeeder.ini file has the following config for UAT:
[dump978]
dump978_enabled=true
dump978_port=30979
When I look into the dump978-fa logs, I see a connection closing and reconnecting when rbfeeder is restarted and UAT traffic now on the RadarBox map.