Ultrakd,
New World amphibians and Old World squamates? I agree with others. Not only do they exist in completely different habitats (different climate, vegetation, altitude), but are both also diurnal, and more terrestrial than arboreal, which means that you would have highly active frogs feeding and making use of the same space, during the same time the chameleons are active-- I think it would be extremely stressful to the lizards.
Additionally, the pathology of both animals may differ greatly considering they are oceans apart, and this may introduce further risks to animals not used to (or immune) to certain diseases, parasites, etc-- just look at what's happening to amphibians worldwide with the mass epidemic of the chytrid fungus, with certain species being more vulnerable than others.
Although most dart frogs in the US are captive bred, and thus no longer contain the same level of toxicity as their wild counterparts, all amphibians remain "toxic" at some level-- they all differ in their chemical makeup-- and who knows what effect that could have on organisms from another habitat, not to mention continent.
I would seriously consider, if you must have a multi-species display, other animals from close geographic areas, at least of East African origin, and most importantly, those with opposing photoperiods such as small nocturnal geckos.
Keeping them separately is still the best option.
Good luck,
Fabián