Well they do seem to work... Has to do with magnetic interference of the object your looking for and the chemistry of the operators body.
You can find vacant (empty) metal pipe and plastic pipe with rods also. Energized electric cable will show up with them to.
"A hillbilly thing", or the body doing the will of the mind---Maybe, however I know of several facility locators working at major, big city electric, gas and water companies that will use rods with good sucess. That bums me out because part of my "day job" is to teach 'em how the high tech locating equipment works. Having a partner that could witch has saved me from going back to the shop for locating equipment or digging up and damaging a buried facility more than once.
The folks I was working with were not pagans, witches or nut jobs either. A couple of them were atheist. So I don't see a "Spiritual" connection.
Never could do it myself with any consistency, however I have worked with several people who could. Back to feilds and chem --I screw up FM radios at certain Freqs and stop wristwatches when I wear 'em (have a drawer full of cheap to mid-priced ones that seized right up. Seems that soil type and chem will affect the results also. (it affects some electrical fault locating equipment too)