Its never a good idea to mix amphibian species. There are a few reasons for this. Cross contamination is one, most amphibians use skin toxins to protect themselves from predation, at the same time they have porous skin that does not keep toxins out. So keeping more than one species together it is possible that they will be poisoning each other. Frogs are simple predators in the fact that most will eat what ever will fit in their mouths, which can include other frogs. A third reason for avoiding keeping different species together is cross infection. Wild caught animals are likely to be carrying parasites and other pathogens. Although it may not seem to be affecting them adversely, it could definitely harm another species, especially one that comes another part of the world.
White's treefrogs, Litoria caerulea are from Australia and the island of New Guinea, while red-eyed leaf frogs, Agalychnis callidryas are from Central America. Both species are captive bred and wild caught. If the frogs you see for sale are big, chances are they are wild caught. I definitely wouldn't mix them. White's are also one of the bigger treefrog species, I have seen them eat mice, so there is another reason not to do it. Then there is the skin toxin issue, another reason to not do it.
If you must mix species, try to keep with species that are from the same part of the world and are closely related. Even then it can be really tricky.