LUCKYSNUCK - Wider tires or wider rims are not always the best answer if taken as a singular variable. Tire width & wheel width work as a unit to afford the best ride, sidewall protection, lateral stability for best cornering ability, traction, and least amount of rolling resistance. Sounds like a car tire commercial, , eh? Actually, this is taken from my bicycle forum when discussions about the exact same thing arises. We always struggle to find the perfect balance. CONTINENTAL & MICHELIN are 2 of the biggest bicycle tire manufacturers, no coincidence same for auto tires. And the theory holds the same. Here is an illustration as it pertains to bicycles, but you might as well extrapolate the same for moto or auto tires.
It is not just the width of the tire or the wheel, the ratio between the two is a bigger factor. Also the reason I would take the tire manufacturer's recommendations on min/max tire sizes is because they know what the stiffness quotient of each particular model of their tires, so they know how those tires will react to lateral forces when turning and cornering. Without the composition of the tire, the tire & wheel width alone are just 2 variables of the multi-legged stool. The wheel manufacturer (ALCOA) can not tell you what the min/max tires widths would be because they do not know the composition & aspect ratio of the tires that would be used in any given width.
IMHO - I would follow MICHELIN recommendations.
BTW - I too was wondering about wider tire sizes if/when I need to replace mine. However, I was mostly interested in wider fronts. What is the need/reason to make the dually tires wider? By virtue of the dually, they are already super-wide? And if wide is really what you want for the rear dually, why not go SUSI (super single route)?