It isn't 99% RH in there. If it were, there would be condensation since the inside of the viv is at least one degree higher than ambient from the lights (glass that is lower temp than the dew point of the air is where and why condensation forms). The meter is giving false data. False data are misleading. Misleading data leads to poor husbandry decisions. Poor husbandry decisions kill frogs. Therefore, RH meters kill frogs.
A couple things about your viv that are going to make it hard to interpret and implement sensible recommendations you'll get about misting and ventilation are (A) the background. It doesn't hold any water, so affects how much moisture is held and then released in the viv.
And (B) the sphagnum layer under the leaf litter is going to mess with the moisture cycle in the viv too. It holds a lot of water and doesn't let go of it very easily, which is kind of the opposite of what we want in a dart viv (a few wet - slightly dryish cycles per day is best, IMO). Note that FG's substrate seems to be pea gravel -- about the opposite of sphag in terms of water holding capacity. Interestingly, in your photos all the frogs are off the ground. I don't keep galacs so don't know what this might suggest, but it may suggest something.
And (C) having the viv in the path of an HVAC vent is going to affect ventilation; how much depends on the exact air flow, I suppose, and whether the HVAC is running or not. Buying and using an IR temp gun would be a good idea to keep a close eye on temps in different spots, since the area near an HVAC vent is pretty volatile in terms of temperature.