If I understand your question, I believe you are concerned with ensuring the effective fault path by determining the overall impedance of the equipment grounding (bonding)?
Obviously, the effective fault path resistance should be very, very low. The only way I can think of determining the effectiveness of this path is by ensuring the EGC's are sized with a withstand rating that exceeds the available fault current that may be expected on the circuit.
I don't know of any other measurements that can be made on the equipment grounding system.
