I know plenty of keepers and breeders who have beardies in pits and aviary style outdoor habitats who live up north in Darwin, Broome, Cairns - way north of the Tropic of Capricorn and not far from the equator who have only two seasons , very hot very wet (monsoon) and hot and dry (winter). Relative humidities are north of 80% , no problems with their dragons.
I get 60- 70 % RH inside my house (subtropical coastal 33 degS) in summer despite running the aircon 24/7 in summer to keep the humidity down at comfortable levels .... never had a problem attributable to humidity with my dragons in 8 years.