I spotted this the other day. I played with it in the simulator, it seems to increase your scout resilience by the designated percentage. When simulating 100 vs 100 scouts, with 30% stealth applied to attacker you only lose 68 scouts as opposed to the 100 you would normally lose.
I have yet to see this be incorporated, I would assume at some point a daily bonus / ingame event perk will give you a Stealth perk much like there are axe/sword item perks
