They call up a temp agency and say "we need X people who have a valid driver's license, a pulse and can piss clean"

Which is incredibly hilarious because surely it shouldn't be too hard to find a volunteer engineer to drive the thing they coded.

Surely?

Disagree. If you screen your test drivers, you no longer have adequate testing. Your test drivers need to be representative (as much as possible) of the general population.

No, Waymo's test drivers aren't supposed to be representative of future customers, they're supposed to babysit the cars until drivers are no longer needed at all. That's why their Firefly prototype didn't even have a steering wheel.