From my research, all I really need to do is enable rxchannel = dahdi/pseudo in rpt.conf (and comment out the current rxchannel = simpleusb/usb entry) and load chan_dahdi.so and comment out chan_simpleusb in modules.conf (and of course restart asterisk).
I finally got my last repeater on the AREDN Mesh and don’t need my hub node to drive a UHF radio any longer