no you should not put things on a tortoise shell it does trap bacteria in the shell and can cause problems, it does bring out the shine of the shell but it also leaves a greasy film so is not good all you really need to clean a tortoises shell is warm water, if you feed your tortoises a good diet with plenty of calcium your tortoises shell will stay in good condition and there will be no need to oil it, if you live in a place where the temp gets really high the oil will heat up and cause your tortoise pain just imagine you putting some hot oil on your nail , the shell is a living part of the tortoises and they can feel when you stroke the shell leave the oil off and just bath your tortoises, best of luck.