I've seen wild carpets, Children's and Scrub Pythons eat green tree frogs (and saw a scrubby eat a White Lipped Green Tree Frog, and have cut frogs of several species out of road killed snakes of many species). All frogs have toxins, but most snakes aren't bothered by most species. I don't know of any snakes which are bothered by the toxins of Green Tree Frogs and I certainly know of many which aren't. Having said that, if you have a sufficiently low level of respect for your animals, you can mix whichever species you like and take the chance; sometimes you will get away with it. If losing a frog will upset you it's not a good idea.