Tillandsias are awesome and work great in a lot of terrariums, provided that they aren't too dry. I've been using a few different species in two different tanks (for L. lugubris, so no frogs, but they don't need more humidity than a L. caerulea) with great success. They only "problem" would be that most species that are commonly available are probably not tough enough to withstand a adult L. caerulea, but they're still make the enclosure look great (and help some with a more stable humidity).