Schefflera, if I understood correctly, has a low level of toxicity. It only becomes dangerous if a very large amount is ingested. I would be far more worried about the pothos. You may want to remove it if he's eating a lot of it. I believe that the toxins in some ficus are located in the bark/sap but this isn't a plant I've kept, so trust others more. How much does your cham eat his plant?
I didn't think of hibiscus before, but that is a good plant choice. It's safe for the cham to eat and pretty hardy. Mine never seemed to care for eating the leaves or flowers, but they're all individuals with individual tastes.