...and can't figure out why not. Any ideas ?

In config file,  verify that "Oil Crater Chance" is not 0
ex: "Oil Crater Chance": 50.0,   give a 50% chance of having an oil crater

also did you set permission to use backpumpjack. without permission, surveycharge will give vanilla minigquarry
give "backpumpjack.use" to default group