While I do agree that people should be aware of any risks in feeding 'collected foods' to reptiles, the degree of risk should also be taken into account. Too often the degree is only qualified with a "don't do it" warning but no real measure. To draw a parallel, one could advise that people should never use roads as people get killed, maimed or injured as a result of doing so.
Snails will void the contents of their gut within 2 days. Those that may have feed upon snail pellets will be dead within 1 day. Rat lung worm is rare enough in Australia that the form of meningitis that is sometimes causes is not a notifiable disease. You also need a well establish population of infected rats in the area. It is not known to infect lizards but there is a suggestion (only) that it may be transported by them. That means no eggs or infective larvae are produced and passed through and for the parasite to infect a mammal it would have to eat the lizard raw, or close to it. The common European garden snail is not listed as a host for this nematode species. Garden caterpillars are extremely unlike to be toxic to lizards. Unless there are dead insectivorous birds (not the result of cat predation) in the same area I don't think you have any cause for concern.
I found it was easier to get snails to go dormant in order to store large quantities for a mate's lizards, than to keep them active and feeding. Just withdraw food and water for a couple of days. Just add water to bring them back to being active. Otherwise they need frequent spraying to keep them clean and viable due to the amount of wastes they produce. Collecting them is easy. I often take the dog for a walk after dark and the number of snails that emerge from gardens to feed on lawns and verges is amazing. They are particularly prevalent after rain or in yards that have run their sprinkler system. Any premises with snails present in multiples of 10 are clearly are not likely to be using snail bait. If you are after very small snails in particular, then breeding your own would be warranted.
Blue