well... we have an underground phone line burried in a trench up the driveway right next to a powerline coming in and every time it rains the phone crackles and buzzes until the moisture dries up so i would say having a cable signal act the same way is not out of the question.
why does it get humid in the room? do you not have the dryer vented properly? we have a washer and dryer located in a 10x7 closed off room without issue. if you do have your system vented you could have a clog in the hose, a leak, or your dryer could be full of lint.
exessive humidity is bad for not just your cable box but could potentially allow fungus or mold to grow and in severe cases moisture could attack the paint, wallboard or wall framing.
i would suggest figuring out why there is exessive humidity in the room instead of trying to bypass the problem, however, this is your choice. you might be able to eliminate the problem with a completely sealed enclosure which is watertight or moving the connection to a new area would work as well. getting a cable re-routed is not a huge deal.
To directly answer your question, no, humidity has zero effect on your cable signal. The worst that could happen, is you could rust or corrupt the connectors. Just wrap them in electrical tape. I'm guessing you have more of an interference issue. You probably a cable line running alongside your 240v Power connection somewhere in the wall, as SSDD says. Try a cable line filter at your TV, it will probably clean most of that garbage out of the cable signal.
i'm not entirely sure what is meant by cable hookup as i've never had cable. (we had dish.) if its a box with connections in it then most certainly moisture could get in and cause problems as jc stated. as far as actually affecting the signal through wire? no.
without knowing any details all we can do is guess.