Helistar, It was said in one of the patch notes that Razuvius' adds were no longer tauntable. Whether it was patch 3.1, 3.2 or a minor patch, I don't remember that clearly.
Junkilo, it doesn't matter who taunts, all taunts give DR for that mob.
I haven't done extensive testing but have suspected since I started tanking (or playing a melee class in general) that for abilities that can't be dodged or parried, Blizzard uses spell hit as opposed to melee hit. This includes Demo Shout, Thunder Clap, Shield Bash, and Shockwave, as well as Taunt.
Since Ulduar opened, it seems that Blizzard is taking full advantage of tauntable bosses by making encounters that require precise timing and execution on Taunts. Because of that, I've personally been using Glyph of Taunt, reducing my chance to miss to 9% spell hit. Depending on the boss, I'll either expect Misery from a spriest or not. If I get Misery, I only need 6% spell hit, which is 158 hit rating. Otherwise, I'll gear up for 237 hit rating for that all important taunt. I also use 20 Hit Rating to gloves now because of the lack of Hit on our gear. Thanks Blizz for making taunts so important then giving us NO Hit. Much <3
Tranquil tree, kamikaze warrior. I will Shield Slam you to the moon.