I have been using vermiculite for 5 years and have never had them eating it are you sure they are getting enough to eat. Do they have a dish of fresh water in their enclosure? They may be just licking the moisture from the side of the hide container and in doing so ingesting a little of the vermiculite, you should also be giving them a little spray from a spay bottle once or twice a week. I'm not sure that putting vaseline on the mealies is good for them and would stop unless you got that information from an expert in herpetology or a vet that is experienced in herps. As for different substrate to use in the hide container I know that some people use peatmoss or perilite. Hope this has helped.