OP, nah, don't worry body jewellery doesn't affect metal detectors!
And to Severo, Vaseline is a waterproof layer that will sit inside the nice moist warm piercing hole and will attract and harbour bacteria increasing the risk of infection. Not sensible at all.
You shouldn't apply any sort of creams, lotions, gels or anything to a piercing, except for salt water. Anything else will harbour bacteria.