The general rule of thumb is never to mix species. If you find a frog you want of a different species, get a separate tank. Mixing can lead to illness and even death in the long run, I have heard it being called "slow poisoning". It is very harmful to all frogs involved, and I definitely sy NO to mixing species.
With that said, I do agree with UncleChester, I'm sure the little guy would like more stuff to climb and hide in, just make sure it's all safe and that he can't eat anything you decide to use. XD