I agree with the post above, it really matter's on the species. Firebelly toads would be pushing it, but with tree frogs and a newt I would say go ahead. Many species of tree frog that are available at pet stores are nocturnal anyway. If you're really worried about the toxin's released by the firebelly toads and newts, I work at my lfs and my owner keeps both in a paludarium with anoles, a rough green snake. Plus we keep them in the same tank on display at the store.