As long as your knife is clean and dry when you put it in the saya you should be fine. But I generally prefer cardboard for work knives. Cardboard is free and takes up less space in a knife roll and if they get messed up I just make new ones.
I use compressed air then a shop vac. My saya stay in the bag, so I only get them for gyuto that will be in use all day. Other knives get a kydex or felt edge guard for the reason above.
Any knife is washed and wiped clean, dried after each use. There is never any reason for there to be "gunk" inside a saya. I personally only use sayas for knives I don't use frequently,
Agree with above...knives should always be diligently cleaned and dried before they are put away, regardless of protective storage method. Aside from gunk, I don't want my blades to rust. I don't take my sayas to work. I pick the knives I am going to bring that day, leave the saya on my display rack, then use felt lined knife guards, or leather sheaths to take them to and from work.