All that time the cuemaker had the shaft hanging to dry went out the window the moment the shaft entered another environment. Wood gains and loses moister constantly regardless.
If you wipe a small amount of moister on a shaft it will not necessarily absorb it it will just evaporate. It is the moisture content of the air around it that determines the moisture content of the wood. It wants to equalize based on temp and humidity.
Here is some interesting stuff on the subject.
http://www.csgnetwork.com/emctablecalc.html
I hang wood in a climate controlled room with 50% humidity and around 75 degrees. This keeps the wood at around 8 to 9% moister content. I can get it lower but as soon as the wood leaves the controlled environment it will equalize to the new environment anyway so I want it to be something general no extreme one way or another.
Again, no one is talking about submerging the shaft in a bath, just a light damp surface wipe that lasts a few seconds. I guess if this worries you don't do it. Also be sure not to breath near you cue either since your breath is around 95% RH. And when you leave the air conditioned pool hall to go to your car be sure to place your cue in a constant climate chamber to limit exposure. I know I am being sarcastic but we are talking about something so Infinitesimal as to be meaningless.