Here are some results David. Sorry it takes so long, I've been doing a lot of care taking for family and haven't had much free time.
pi@raspberrypi:~ $ rigctl -m 1020 -r /dev/ttyUSB0 -s 4800 -P RIG t
pi@raspberrypi:~ $ ls -la /dev/ttyUSB0
crw-rw---- 1 root dialout 188, 0 Aug 26 16:24 /dev/ttyUSB0
At the moment the system is stand alone. Once I get all this figured out, I'll burn a bigger SD card and do it all over again, so I'm just using the root account.
I played with the rigctl stuff and was able to read the rig's frequency and make changes, so it seems to be communicating over the cable. Of course that was the case with Fldigi, so no surprise there. All I can think of is somehow Direwolf is having a permission problem. Either that, or some sort of group membership problem.