It certainly sounds like a good safe method of destroying mites... the oil would block the trachael spiracle (breathing apparatus) of the mite. I'm not sure if olive oil might have a detremental effect on the snakes' sloughing process though, if it was not thoroughly washed off. Obviously you did wash it of properly, but if others were to copy your method, I think particular care should be taken to ensure that the snake was completely free of oil after each treatment.