This is completely wrong, Vengeance no longer has anything to do with your health pool.
Source is here:
http://us.battle.net/wow/en/forum/to...?page=186#3701
As for the Relic, I'm not saying it's worst decision. But I think it was a good choice. If you're great at rotation your shield blocks and shield barriers you should be fine using this trinket. This is a very good trinket for offspec, lolzheroic runs, and perhaps even Challenge modes. But for raids I would stick to the more traditional Tank Trinkets.