Since my highest character is about 944 and already done with all challenges, I cannot say - but I would assume that it would be so. You probably still have to look out for oneshot-mechanics, but other things don't bother as much. For example, I have survived a hit from Karam on my affliction warlock with item level of about 930 (no prydaz). But if you let yourself be kicked off the platform in the tank challenge, or don't pay attention to your npcs and they get wasted by adds, then the encounter will fail anyway. Though you will probably burn through the 1st boss fast enough so not many of these things would be happening. ^_^
Though for healers, overgearing the challenge makes the last stage harder because you have to keep your health lower than the usual guides suggest.
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Ret was a bit harder for me with about 910 item level, but still, got it in about 10 tries (which I mainly needed because I don't play ret at all). When you know how to react to mechanics, you only fail due to really bad luck in this encounter. Meeting DPS requirements was not that much of a problem.