It may be possible, but I watched enough to conclude that ESTLCam likely downloads GRBL motion control into the UNO, then uses external Stepper Drivers (rather than a Gshield) to interface the steppers.
The tinyGV8 interface language and serial I/O control is different than what GRBL defined way back before tinyG forked from GRBL.
Similar CAM functionality for tinyGV8 is provided by Chilipeppr, which started focussed on tinyG but was enhanced midstream to have a GRBL flavor.
So, if ESTLCam is open source, you might be able to create a tinyG version, I would guess with non-trivial programming effort.