Yes, Iuz is one slimy and calculating entity, but I got to go with Cuthbert here. That stance disciplinarian won't take "no" for an answer. He'd wear down old Iuz, wacking him about his head with his handy-dandy cudgel.
I'm curious why Wee Jas would be brought up in the initial post? She has no stake in either god getting one over on the other. They are even all different pantheons.
Iuz would probably have the edge in an avatar vs avatar fight on the Material Plane, even with his demi status, but Wee Jas would back St. Cuthbert without blinking an eye. Law calls to Law, in her book.
Iuz probably wouldn't last in a battle with the Saint, as a lesser god is more powerful than a demigod. And if Iuz tries stuff like bringing demonic or undead help for the fight, St. Cuthbert is well within his rights to do the same with angels and lawful creatures.