That's good reasoning.In my qt I always use paper towels to keep an eye on their feces. Thats usually the easiest indicator that something is wrong.
I would imagine dart frogs can be quarantined the same just on damp towels.
I prefer to be able to gauge behavior, too, which will be affected by such a setup, especially (I would think) with more skittish species -- I really can't imagine housing thumbs in a sterile box for long, but I'll admit I haven't tried it, or even looked into others' experiences doing it. Seems each method of those two have their own pros and cons, and the judgement will depend on the keeper's relative concerns.