Mixing species usually isn't a great idea. However, i've seen several instances of mixing emeralds with dart frogs. I know Baltimore Aquarium has been doing it for over ten years, and i've seen it in a few other places as well. I figure the boas COULD eat the frogs if they chose, but everyone i've talked to who has experience houseing the species together said that they've never had a problem wih it.

Still, I wouldn't try it unless you're willing to take a decent sized risk and/or have experience with both species, i'd also reccommend talking at great length with someone who has housed them together.