Some aquarium hoods have glass separating the light from the tank. Does this have anything like that, or is the light just exposed to the air? If it has a glass shield and there are no areas up in the fixture the frogs could get into then it may be usable as a top with some modifications but if not I'd probably just get a glass top and light strip. If you want to use the actual light you may be able to set the whole hood over a glass top still. If you just have the one tank I wouldn't bother with a misting system especially on a small tank like that. If its part of a whole rack of tanks thats another story but I'd just hand mist that puppy if you have less then 10 vivs
Save the $100+ for a misting system and use the money to pimp out the tank in sweet plants and hard-scape materials. Could do a drip wall with a tom's aqua lifter pumps...and/or a waterfall.