Russia and China are not the point. We were in a cold war with them for years, and no one questions the validity of that cold war against them.
My point is that a trade between Iraq & Syria — oil in exchange for weapons storage — would be absolutely sensible. Not only would Syria be able to handle it with no questions asked, but they would also be able to handle it with proper technology & handling procedures.
And not only “could” handle it; they could have EASILY handled it.
With respect to the each other, of course they were rivals. They were competing for regional dominance and to be the standard bearer of a shared ideology.
With respect to the west, they were allies. Whatever rivalry the two countries may have had was nothing compared to existential threat they saw (see) in the United States.
Same with Syria and Iraq... or Russia and Iraq, or China and Iran, or North Korea and Syria, or imperial Japan and Nazi Germany for that matter. America is everybody's worst enemy. And the enemy of your enemy is your friend. What was it that brought the Baathist socialists in Syria and the Iranian Shia into their currently alliance, other than a mutual hatred of the west?
The reality of the situation is, both the Iraqi Baathists and the Syrian Baathists stood to benefit greatly from embarassing the US on the matter of WMD. Of course they worked together toward that end.