@mitu Sorry for the late response!
There were indeed no events when I tested with evtest.
I completely removed the keyboard again, rebooted and started Pixel. I again paired the keyboard, and made sure it worked in Pixel. Then I rebooted into ES again, again no keyboard..... some kind of weird inspiration made me go to the Retropie Config (you know, where the setup.sh is started) and, much to my surprise, I found that after a few button pushes the keyboard started working! I have no idea what went on and why it worked, because apart from opening setup I did nothing differently from the first time. After leaving the config I started evtest again (via the remote console) and actually this time around the events were showing up! The keyboard actually started to work!
Soooo happy now, as after adding the proper event source to the moonlight config I actually have full keyboard support there as well!!!
Thank you again for your help and patience @mitu !