I believe they can add humidity to the O2 line to prevent that...?
It _definitely_ helps to run the gas over water (a humidifier), yes. But as far as I know, that still only mitigates a little of the dryness - because 100% Oxygen just dries membranes out among other things. It is the _percentage_ of oxygen that is relevant.
https://science.howstuffworks.com/question493.htm
(Is It Harmful to Breathe 100 Percent Oxygen?)