Yes, my current avatar is a Dendropsophus leucophyllatus. I have written a few short articles for a new series to be published here at the frog forum. The series is called "Meet the Frog" and will an introduction for most people to many different frogs from around the world. The first one is about Phyllomedusa hypochondrialis, the second is about Dendropsophus leucophyllatus.
I think Dendropsophus leucophyllatus will work nicely with cardinal tetras, Paracheirodon axelrodi. But I would consider how are you going to feed them? Remember crickets drown easily. You could use Drosophila hydei, but you need to have ventilation for treefrogs, while making sure the flies can't escape. In small enclosures such as critter keepers I use paper towels to do this. They are placed between the top and the bottom of the keeper. But how do you do that with a 20L or 29-gallon tank?
Also I have never seen the giraffe phase for sale.

Here is Danté Fenolio's care article on Dendropsophus leucophyllatus.
Click here: Clown Treefrog Care and Breeding