If a substance that forms an impermeable layer on the body, preventing water from coming into contact with the skin, has been applied, it must be removed prior to performing wudu. Since Vaseline typically doesn't form such a layer, wudu performed after applying it is considered valid.
However, if the specific Vaseline used appears to be forming an impermeable layer on the body that prevents water from making contact with the skin, wudu over it wouldn’t be valid.