You are 100% right. The oil itself will not allow it to rot out. And yes ... It is a PITA to drop the oil pans on these trucks ... but not quite 7 hours worth.How incompetent are their mechanics? If your puke bottle is overfull it will dribble oil down and make it look like the oil pan is bad.
And it is a NIGHTMARE to get the oil pan off the 4x4. You have to raise the engine. I don't know why they used studs (only a couple of them, too) but since they did, you really have to lift it up quite a bit.
I would inspect the pan myself, carefully retorque the pan bolts, empty the puke bottle and forget it. If it's covered with oil like most cummins pans are (from not emptying the puke bottle or not having one) the oil will prevent the thing from rotting out no matter what nasty rock salt and ocean water you flog through.