Yea, outdoor use is just common sense. There really shouldn't be a problem. I've used all sorts of gear outdoors with no problems resulting from it.
You just need to be aware of the weather forecast and then make your plans accordingly. You would be making the same arrangements based on the same concerns with your instruments, PA, and other gear as well. Lighting would just be another element to add into the mix.
A humid night indoors could be just a detrimental to humidity outdoors (possibly even worse since there is usually little air flow indoors).
Go with the LEDs. No lamps to change, low power consumption, low heat, lightweight, flexible programming options, desired results. They're the best option for wash lighting without the use of good old par cans and dimmers.
Architectural lighting could always work, but you're starting to talk big dollars. Chauvet offers some outdoor-rated LED equipment, but it's quite pricey anyway. Elation has some stuff that will do the job too.