I used to have an ultrasonic fogger hooked up to my 30g vivarium and it would keep me from ever having to mist the tank down or refill my reservoir. so plenty of water comes from it. so, yes, it "could" be considered a cheap substitute for a misting unit.
my current 110g vivarium has both a fogger and misting system though.
here is a pic of my 30g and fogger system:
unit
effect
effect in my 110g
