Predictably, after his defeat in the Gulf War and with the star of secular Arab national socialism fading, Saddam has turned to Islamism to bolster his personality cult (Iraq builds 'Mother of all Battles' mosque in praise of Saddam). Meanwhile, bin Laden's religiosity is mostly for public consumption -- his own kids get to watch TV and play with computers. But the religious crap certainly makes a good recruiting tool.
The alliance between Saddam and Osama is no more suprising than the alliance between Hitler and Tojo, or the one between Roosevelt and Stalin for that matter. The benefits flow both ways. Osama couldn't organize a piss-up in a brewery, but he makes great recruitment videos, and he's willing to do the "ascetic in a cave" thing the Arabs love. So, Osama provides the kamikaze killers, and puts out the talking points. Saddam's end is money, organization, intelligence, and advanced weaponry (i.e. anthrax). What a team they make!