They are like ADC values but the way Marlin does the sampling they are summed/averaged so they behave as if they are 14 bit values.
What hardware are you using? I am guessing an encoder based jog wheel? I can see the value in a jog wheel but I would be a little concerned it might not feel like what you are expecting. Either way I am interested to hear what you find.
Also, not to discourage you from the analog joystick method but if you already have an external processor you could inject gcode like the other joystick approach I’ve seen.