mikey, there is nothing 'stupid' when it comes to bees, and i appreciate your questions and posts. many things puzzle me as well and don't think to ask.
bees 'heat' and 'cool' the hive, they can reduce the moisture. they can heat and cool a hive. it's amazing. i see reduction of moisture mostly when the nectar is coming in, and nectar turns to honey. bees can regulate temp and moisture.
we can get very humid in wisconsin. lately it's been an incredible up/down in temps, rain, and humidity. temps reaching 104 d f, with high humidity, rain and torrential rains, and then some days temps barely top average temp for us. it's been raining here for days. i see the bees bearding, fanning, and during rains, not so many out the front of the hive.
to answer your question, if bees are caught in the field in a thunderstorm, some may make it back, some may not. when bees get wet, they can't fly.
on the landing board, in a downpour, wet bees entering a hive and adding moisture? to be honest i can't answer that question, don't know if anyone can, but i wouldn't think they would add extra moisture to the hive. it is when they are confined that moisture is added to the hive.
maybe keith (apisbees) has a better answer for you than i do..........thanks for asking mikey!