i don't think it will do much if you vent your ship since the boarders will probably have some sort of space suit.
though it would be cool if you could close the blast doors and the boarders would have to cut through them.
From what I've read and understand about the docking collar; it forms an air-tight seal.
In order to avoid having to wear a suit 100% of the time in your ship, your ship would then have to have a vacuum chamber that can be filled or depleted of air.
It would be an excellent addition to Star Citizen and very realistic if ships had air chambers and you could deplete air levels in certain areas of the ship. Then, only boarders who donned breathing equipment would have a chance at success.
It would allow them to steal your cargo without harming you, if you're willing to let them take it without a pistol fight.