I have stored pistols for years in leather holsters with no problems at all. I once had a Bianchi, John Wayne commerative holster and gunbelt that I used as a decoration really. I kept a Mitchell Arms SSA in that holster for ages with no special treatment at all. I'd take it out once in while, wipe the dust off, sometimes with a silicone rag, mostly with a dry cloth, and put it back. That gun never had a speck of rust on it. Right now my Ruger bearcat hangs from a nail, in it's leather holster on a belt, ready to go. No problems at all.
Should you do it? Probably not. I'm not saying it's a good idea even, just that I never seem to have a problem doing it.
Most of my handguns rest in my safe, wrapped in old cotton socks, more to prevent scratches than anything else. I don't do anything special to them other than take them out from time and check them.
Shotguns and rifles, are just wiped down and put in the safe. No problems ever.