They used to recommend a full synthetic oil that met a specific Mopar spec number, but have since rescinded that recommendation. They do however now tell you to follow the "severe" service schedule if using E-85 more than 50% of the time.
I think it's more about the ethanol washing down past the rings diluting the oil than it is anything to do with the combustion byproducts of the ethanol, which is more benign than gasoline combustion blow-by.
My dad and I both drive FFVs, and both him and I have noticed the oil stays much cleaner running E-85 than it does running gasoline. I've got a tick over 3000 miles on my oil change of Pennzoil Platinum, and it's still so clean it has the slight greenish tint to it yet. My dad runs Mobil 1 in his, and at 5000 miles it's still perfectly golden color. Not a trace of darkening.
Whether that means anything or not is not certain, but running either engine on gasoline for a normal OCI would definitely show considerable darkening of the oil.
