Sorry for the delay, I only just had the time to try again. It turns out I should have read the description on the DietPi software page ((resolved) Cannot log in to the MySQL server):
VNC servers start automatically during boot, unless you have selected Desktop as a dietpi-autostart option.
I’ve now selected auto-login only, and headless VNC to desktop works now. Sorry about that, I simply didn’t realize there was a page detailing all the optimized software packages. Thanks for all the help!