I had time to try again, and this time I was able to complete a flight with the Saitek Radio panel working in Linux (OpenSuse 15.2). The solution I used was the one in
https://github.com/hdd-robot/flightgear_saitek_radio_panel. (No, I have nothing to do with that sofware.)
The solution was -as usual- simpler than what I first thought - all I had to do was to use the F12 view and flick all the active/standby buttons once before running the saitek_fg program. May be the previous segmentation fault problem is just an initialization issue.
Although it still does not work quite out of the box, I have to first use xinput to resolve the radio panel acting as a mouse, and then use dmesg to make certain that I am addressing the right hidraw device, and created a simple udev rule to make it unnecessary to run the program as root.
What works: the basics. The displays light up and display the selected frequency correctly, except for the ADF. Using the controls on the radio panel change the frequencies in the sim, and this is visible in the radio stack.
Issues: I could not figure out how to change the VOR radials, except via the F12 dialog. When tuning down the frequency hops up if crossing a full number from up to down, e.g. if tuning down from 122.02 it will change to something to 122.97 when crossing the 122.0 downwards. Upwards tuning seems to work. The Saitek radio panel does not display the frequencies for ADF, but they change correctly in Flightgear when tuning from the panel.
Of course, I did not find it the easy way- since the panel seemed to work with the Cessna 172 (which I never fly), but no other aircraft I tried last time, I initially thought that the software might be particular to the way the radio equipment is implmemented, This turned not to be the case, in the end, but I did end up figuring out how to change the radios in my DC-3, and at least now my (t)rusty Dakota has more radio equipment visible in the cockput