(Replying to my own question.)
The k2radio article describes how this works. The drone control app on iOS talks to a remote server for mapping info. The Feds feed geofence info into the control app servers and that gets delivered to the pilots & their drones.
"AirMap and Skyward now obtain wildfire information directly from Interiorâ(TM)s Integrated Reporting Wildland-Fire Information (IRWIN) program, and immediately transmit it to drone pilots through AirMapâ(TM)s iOS and web apps, AirMapâ(TM)s API, and the GEO geofencing system included in the DJI GO flight control app."
I'm going to make the giant assumption that enough drones operate in this manner to make this worthwhile.