The thought in the hobby was originally that the frog could fall into the pitcher and be consumed. That's since been proven false. In fact, quite a few hobbyists are keeping darts with nepenthes species and they not only have not had any problems, but find their dendrobates spending time hiding inside the pitchers.

Just keep in mind that wen adding a carnivorous plant to an enclosure, that you are adding another mouth to feed and plan accordingly.