Ground is ground. I wonder why they want the BitRunner ground to be on the Z axis. If the Z is grounded then any place on the Shapeoko that is also grounded? You could use a multimeter to determine if the router body is grounded. The Belt Z does run on plastic v-wheels so it is possible the router is not grounded. I have a Dewalt as well and the plug is only a 2 prong polarized plug so the router is not grounded by the power cable but may still be grounded by attachment of the router clamp to the Shapeoko. So it might be best to drill a hole and tap it to make sure. An alternative may be to use one of the Z motor screws to ground the BitRunner. That way the wire will not be moved up and down on the router mount.
I tried attaching it in the slot where the bolts inter on the face - the ring connector is a bit too large to fit by a mm or two - I could force it down, but that would be a problem down the road.
I tried in the clamping slot but the slot doesn’t clamp down on the ring terminal so that’s a no go.
Pretty much every piece of exposed metal on the Z-Axis has continuity with every other part. Even the 2 steppers have continuity.
There is one bolt holding the carriage halves together that doesn’t, but everything else does.
If this something need to correct? I’m assuming the holes on the plates aren’t powder coated so my suspicion is that the current path is through the steel plates that the router clamp is bolted into.