All sources that I have reviewed indicate that ginger leaves are non-toxic for amphibians. Some south Asian frog species love to roost in them, so I think you are safe. If this plant is new to the terrarium, however, just keep a sharp eye on your guy for any signs of unusual behavior that might indicate a skin sensitivity. If in doubt, remove the plant and observe your frog for a week or two before deciding when and if to place the plant back into the habitat.