I would like to point out that omega mutants are simply born omega as it means unlimited god-like potential determined by their genes, not actually developed power level. Most confirmed omegas aren't all that impressive at the levels they actually reached.
All traits usually ascribed to omega mutants such as sub-atomic manipulation of matter, the potential to survive one's physical body, extreme energy manipulation, some kind of reality warping etc. are really fan-made and few confirmed omegas actually displayed them.
The only way to tell with certainty whether or not a character is omega is to have it explicitly stated on panel. Many characters, like magneto, chuck and exodus are strong candidates, but have never been confirmed beyond doubt. In fact, even the SW hasn't been confirmed as one to my knowledge.
Therefore, the fact that iceman is an omega means jack, cause he doesn't have the power or feats for this battle. He is way out of his league.