People have used these in the past, in a pinch, but I cannot recommend them because:
--the gel is toxic and if your chickens got into it, would be a disaster.
--would be an expensive way to address the problem over time.
--if you have humidity problems, you have a design issue that you need to address to really fix the problem. For instance, you may not have enough ventilation, which is really important to have. Or you are directly on the ground, in a wet climate, so moisture is rising into the coop. Or you have a buildup of poo, which can put off a lot of humidity.
If you can give specifics about your coop, size, number of chickens, ventilation holes, etc... we could probably give you some better answers for addressing humidity.