frogs & chameleons
I too have kept some of the larger chameleons, before I switched to darts due to space issues. Most of the larger species would be horrible
companion animals for dart frogs, in my opinion. Most need more air circulation (like Josh said), so mesh cages are usually used. Depending on the species, most will fight with each other and do get upset at their reflections (usally males fight males). On top of this, if it is small enough to fit in their mouth and moves... they will probably eat it. I have seen chameleons take rather large prey in the wild (didn't see this in person, but in videos, pictures, books, etc.), and some of the larger species have been known to take small birds... so a small frog that is hoping all over the place might look like an easy target
As for the dwarf chameleons and the mantellas... I think they have basically identical care requirements. They live in the leaf litter just like a lot of the mantellas, and also live in the damp forests as well. The high humidity would just make them breed from what I know. I would do more specific research on the specific species, so I could match one chamelaon and one mantella that have the most similar living conditions. But in general you but the dwarf chameleons in a planted terrarium with leaf litter and branches to walk on. Then you mist 1 or 2 times a day depending on your top and local humidity/etc. That sounds like the same for a mantella to me, minus the small branches... but that won't hurt the mantellas.
Also, I have been talking to a zoo keeper that has kept dendrobates with eyelash vipers... and they do eat them from time to time. I thought it was very cool that they had them together, made a cool looking tank. After asking about it, I was told that they have had mixed results with it. In one tank with auratus and an eyelash viper there was never a problem, and in another with azureus instead of auratus the snake ate a couple of them. So I wouldn't do this myself, as it jeopardizes the frogs' health (or should I say lives lol) way too much for my liking.