I have been using full screen tops for my frogs for years now with no problems. The only problem is keeping the flies in with screen tops, because melanogaster can usually wander right through the screen. All I have done to fix this is to superglue a sheer fabric on the inside of the screen and attache the screen to the tank with velcro. This makes it impossible for the flies to get out.
As long as you have a water feature in your tank (small pond, waterfall, or even a mister/fogger) the humidity will stay high enough for the frogs, and the extra ventilation is good for them. This method was given to me by Ian Hiller, who has over 20 experience with frogs, and I have never had any problems. I also have the added benefit of being able to see my frogs because the tanks are not all fogged up.
As was stated earlier however, the terrarium in question sounds like a critter cage. These are made of thin glass not designed for the weight of water. If you decide to use it for frogs be very careful with what you put in it, and do not consider moving it with anything still inside.
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1.1.3 D. azureus
0.0.8 P. bicolor
0.0.7 D. auratus (polka-dot)
0.0.3 D. auratus (blue)
0.0.3 D. auratus (kahlua and cream)
Shannon