I had an idea of creating a vivarium with carnivorous plants and maybe a tree frog or two. Can this be done or will waste from the frog effect the medium the plants are in and thereby harm the plants.
You might be okay provided your tank is large and you first create/establish a bioactive substrate (substrate possessing sufficient flora and fauna to break down the waste ... should find info if do Google search & research). A bigger concern will be the cps, themselves...
Most of Sarracenia require a cool winter rest to remain healthy for the long term.
All vfts require a chilly dormancy for long term vigor.
Many Drosera and Pinguicula have a dormancy period.
Nepenthes fall into two main categories -- highland (requiring cooler temps) and lowland (requiring warmer temps).
Both Neps and Sarrs will easily outgrow all but truly huge terrs.
While cps do enjoy humid conditions, they also want good air circulation.
By and large, cps as a group require strong light. This will affect temps in the tank (though by how much will depend on a number of factors) and may raise the temp above what the frogs will want.