This is like running back and forth across a country highway with your eyes closed - you'll probably be fine but eventually something will come along and hit you. My main misgivings would be parasites of different geographical origin (mainly form the Cane Toad to the frogs since he is likely wild caught), possible disease issues (though at this point that is less of a risk) and definitely toxins from the Cane Toad should one of the Pacman frogs try to bite it.