It turns out I was able to solve my own issue through some research, a large dose of stubbornness, and a bit of experimentation. In the hope that my solution might help someone else with a similar problem...
I edited /etc/systemd/system/x11vnc.service, inserting the -nocursorshape parameter into the line that executes /usr/bin/x11vnc.
I've thrown several VNC clients at it and my wireless keyboard/touchpad's cursor is now visible on the screen while using each of them. There might be a tiny bit of lag as a result of the fix, but nothing troublesome and easily worth it to have a visible cursor using VNC via the Stellarmate app on my iPad!
Of course your mileage may vary. Also I can't guarantee this doesn't have a negative side-effect that I haven't yet encountered, or that the fix will work properly with all hardware/software combinations.