Also keep in mind, that because of all the sockets, armor, and stamina, the frost resist belt is one of the better pre-raid tanking belts.

As much as I hate using resist gear for your regular tanking set, there are only 4 belts in the same ball park and only 2 of those 4 are clearly better.

1 of them requires emblems, and the other 3 require lucky drops from heroics.

But back to the main topic, frost resist gear isn't necessary for current content, but it makes it a lot easier. If you're having any kind of trouble on Sapphiron, gearing up the dps in frost resist makes the fight a cakewalk.

If frost resist gear helps the main tank, the difference is small enough that the healers won't even notice if you just wear regular tank gear.