That is a good question. Depending on the type of worm and how efficient your system processes the chemicals in the herbs as well as where the worms are all factor in. As for resistance some are effected more then others and more easily then others by different products I would imagine.

People have been using the standard herbs for thousands of years. They are still killing parasites galore so I doubt it.

The way bugs would become resistant is if some of them had some kind of strength that enabled them to survive the herbicides, then passed on those genes to their descendants. But if none of them survive, then there is no resistant strain built up.