In short, no.
I'd advise you(or your shooting pals) buy a good Bore-Store bag, a treated bag(that reduces moisture, dust, water), protective case-rug or a small gun safe.
To store weapons in holsters is unsafe, may lead to a mishap-AD-theft & may cause wear on the firearm after extended use.
PS; I'd also advise he check his holster & gear often. Broken snaps, loose straps, worn parts could also cause major problems in a real use of force incident.