Looked it up. They have 19 submarines. Not very useful in a land war (they aren't missile subs, they're diesels for anti-ship operations).

It would seem to me to be ill-advised to cross Iraq and attack Kuwait. We would see them coming. It would be a "Highway of Death" all over again. Total massacre.

en.wikipedia.org - Highway of Death

That might whip-up some national fervor, but it would also remove them from the top tier of military powers in the region. Their military would be all but annihilated.

Though they could use their subs to harass (directly) sea traffic. Diesels are very quiet, and difficult to detect. When we engage in wargames with allied nations, sometimes one of their diesels gets close enough to score a "kill" on one of our supercarriers. They are more than adequate to patrol coastal waters, and the entirety of the Gulf.

I think the bigger worry would be China getting more of a beachhead in the middle east at Iran's invitation. But that might happen anyway. There's nothing stopping Iran from issuing such an invite tomorrow.

Plus nukes. As Perun pointed out, analysts suspect that an attack on Iran's nuclear programs would likely result in an acceleration of them. And once they get a nuke, if we've mostly wiped them out, they might be encouraged to launch it on an ally (most likely Israel). The only thing that would be safe is Jerusalem because of the Al-Aqsa Mosque. They wouldn't risk destroying that.