I was recently in Sohm Al with a tank wearing a level 49 piece of gear. The rest of his stuff didn't measure up either. He'd die in two to three hits, and while I may not have been the best healer in the world there was no way I could have brought him through that dungeon.
I was going to mention something about it, but he went on to make some other questionable decisions so I simply left, after the three wipes from the first pull of course. I simply don't think he was prepared properly as a tank.

I don't think dungeons need a minimum ilvl per se. I think people need to be better indoctrinated into their roles.