Kaity, I've done it myself, but only when pinched for flies. An in tank culture presents a danger of the frogs getting stuck in the media. The media gets gooier because of the humidity. If there are enough old casings, this is probably not a danger but I have personally lost a frog this way while on vacation once. Another solution would be to put a circle of bridal veil mesh over it so flies can get out and frogs can't get in.
If you do decide to do this you will find that the tanks humidity can actually stretch the life of the culture and extra month or more! This can lead to extra mites in your viv. Up to you to decide if that is a problem or just more nutrition.
One last concern is that you will not be dusting flies during this time. Even if you do dust some and throw them in, Your frogs may be full and ignore them.
That's the pros, cons, and dangers as I have seen them.