Armor has no effect on magic damage, which most raid-wide damage or healer-affecting damage is, discounting stuff like cleaves I guess. The example in question (Blistering Cold) would not be mitigated by armor.

Yes, Beacon lets paladins basically cheat and heal both themselves and the tank at the same time. As a shaman, I can, will, and have eaten stuff, died and popped back up. Some people say only baddies who plan to die take Improved Reinc to be able to ankh every 15 minutes; I say shamans who have to follow a tank around even if it means getting puked on by a big ugly boss sometimes have to die, and its good when that isn't a deal-breaker. Our first BP kill, and our first BQL kill both, I died, popped back up, and tried desperately to keep everyone just above dead until we killed the boss (and I had pretty much given the tanks up for dead the very second BQL dropped that first time). I don't usually do it INTENTIONALLY though, mostly because it wipes out my mana and makes me semi-useless. I have intentionally let DPS die many times though, because sometimes I just can't save everybody.