Well, i have to disagree.
His gear will chance with ICC-loot. I have atm less then 3% hit, in my ICC-Avoidance and my ICC-Armor-Set its less then 1%. He will loose a lot of hitrating, if he swaps out the necklace (marrowgar) or belt (emblems).
Hit as tank is complicated.
It a waste, if you have 1 or 2 Mutilation-Rogues or Hunters in your 10m, that supports you with Tricks of the Trade and Misdirection (or in my case up to 3 Muti-Rogues and 2 Hunter in my 25m). But then, the RD-glyph is required in a lot of fights. Thats a hard trade off.
You can skip it, but not forever. There is no "best in slot-for all situations-gear". Its no problem to change your gear, if you want 5% or even 7% hit and take Glyph of Salvation instead of RD but if you gear strict for migration and avoidance, you dont need another -20% dmg cooldown and TPS-Stats to compensate the Hand of Salvation-Loose.
And i personally dont know a situation, there you need 3 cooldowns with 2min CD and at least 20% DMG-Reduce or Auto-Guardian Spirit. (Dont answer Sarth 3d <.<)
Sorry if my english is'nt so good, it's not my natural language.