Actually, Defense only applies to the same kind of attacks that Shield/Absorb does. The only survival stat that really matter for PvP is Endurance. But there's an exception, the damage transfered to you through a putting a guard on someone can be avoided by defense and mitigated by shield and absorb. If you go with tank gear for PvP, you need to focus your actions around guarding someone, probably your healer, and to be effective you probably have to communicate with that guard target so he keeps you alive.
For a tank, I would say you either go full tank gear with heavy usage of guard, or you go with DPS gear. Personally, since I solo queue, I went to DPS gear route on my main (Shadow tank).