Automotive ground shift phenomenon
My question is this: is this phenomenon something that truly exists, or is it simply an internal "old wives tale" with little to no basis?


Well, do the math. If you sink let's say 100 A into a steel conductor of let's say 50 mm² diameter, what is the voltage over 10cm of that conductor due to ohmic resistance? 

So yes, Ohm's right, and if you put a lot of current through anything that is not a superconductor, there will be a potential difference.


  What is the fundamental electrical principles at play here?


Ohm's law

Furthermore, your ABS example highlights another aspect: If you've got something that is a switched load, you're not putting a DC load on your ground conductor, but (also) an AC load.

The resistance for AC is not inherently the same as for DC – for example, an ideal coil has 0 Ω resistance for DC, but for AC, it has \$j\omega L\$ Ω - that is, the higher the frequency, the higher the effective resistance. 

Such reactive properties depend on the geometric shape of your conductor – you might even have bad luck, and due to elegantly hitting a resonant frequency of the whole battery – supply cable – load – chassis return system, you get a voltage extremum at exactly the frequency your ABS works at.