I've never even heard of that wood so I can't comment specifically on it. However, if you know it to be toxic to mammals, it would seem like a bad choice for amphibians, don't you think?

On the subject of space, in reality you can't take the floor space and "divide" it per frog. I know basic care articles sort of imply that you can, but that's not how the frogs work. 4 leucomelas in twice as much floor space as 2 leucomelas is actually a far superior situation.

Now to your specific situation. Please do not try to keep a leuc in a 10 gallon vert. These frogs are large (for darts) and they need a good amount of space. A 10 gallon vert for a frog that large is definitely too small in my opinion. Not that this is an ideal suggestion, but you would be much better off keeping that one frog in a 10 gallon horizontal - this species climbs, but they spend a lot of time on the ground too, and the quality and availability of vertical space is generally inferior, especially when the terrarium is put together by a newcomer (no offense intended, just being factual).