When you say arboreal, are you thinking about the larger darts, smaller frogs, or thumbs? I think the general feeling is that for the larger species leucs will use more of the vertical space than other larger frogs. I have some young tincs that climb all over the place, but the terrarium is built more in terraces than a sheer back wall with tall plants so it is easier for them to get their not-always-so-graceful selfs up to the top of the vivarium. I have one frog that perches on a piece of corkbark about 1" from the top of the tank. So, I guess part of the answer depends on how you are constructing the tank and what size of frog you are interested in.
