Yes, as mentioned in #3, most parts of the USA have no use for them. This is especially true on the east coast where humidity is just as much a problem as the temps.
As for mold control, there're tablets I buy for the condensate drain pan of my water-cooled 'a/c'. Might these be used? I'm not familiar evaporative coolers so an expert should weigh in before you purchase. Just a thought.
Not applicable to your concerns but of possible interest:
Somewhere there's a thread in which the cooling system of a theatre in the SE (Georgia?) is described. IIRC, the system was installed in the 1920's. It was hellaciously complicated and required close monitoring but worked quite well given that the temps and humidity both were often in the 90's. Unfortunately, I can't remember what it's called so I can't search for the thread. IIRC, its claim to fame was that there was no compressor.