Dimilin is a tradename for diflubenzuron, a pesticide. It works by inhibiting the production of chitin, the component of the exoskeleton of insects, etc.--if they can't produce that substance, they can't grow, so they die. If I remember correctly, it's an extremely safe chemical, often used outdoors to combat insects due to its non-effect on the ecosystem.
It should be safe for axolotls. Search on dimilin on the forums and you'll see a couple others who contemplated its usage.
Let us know if you hear back from the colony about it. It's very effective against the kind of parasite you've been discussing--one of the best (most effective) chemicals against them.
I'm sure there is some information online about it if you search (you might have better luck searching by the chemical name), but I'm pretty sure everything you'll run into will say it's more or less safe--chitin production isn't done in axolotls, so inhibiting it doesn't have an effect. It's non-mutagenic/non-carcinogenic as well, I think.