Another white lipped tree frog is the absolute ONLY thing that will live in there.
ANYTHING else that is put in there WILL DIE!!!!!! Frog mixes always result in death. A poison dart frog in there would not last long.
Plus, the bacteria in the systems of each animal will not be compatible with each other as they come from different continents. It is much like when people get sick from drinking the water in Mexico... the Mexicans have an immune system that can deal with their native bacteria.... but we cannot. The is called New World Syndrome... and another example of this occurred when the Europeans came to the Americas, and introduced what were simply routine non-serious diseases to them, that actually wiped out many native North Americans who had no immunity to them whatsoever.
Here is a link on New World Syndrome. Read it! It will save the lives of your frogs and your money:
http://www.livingunderworld.org/amph...icle0007.shtml
Plus, here is another article about the physical dangers of species mixing:
http://www.caudata.org/cc/articles/M...isasters.shtml
Species mixing alwys results in death sooner or later. Don't let those silly pet store mixes fool you. The animals in there are never in there for longer than a few weeks and either sell or die. Plus, animals from these setups often die a few months down the road as a result. Also, those who tell you they have had a mixed tank"work with no problems" are either lucky, lying, or gave some half-a$$ed and/or incorrect diagnoses to deaths that actually were a result of the species mix rather than their half baked and uninformed excuses .
Darts do best on their own.. especially if one is new to frogs. The key to success is to stick to a single species.
Nobody has ever convinced me that the animals will benefit in any way from being in a mixed tank. Therefore, I see no reason for it.
Good luck.