I know it's been a few months since you posted this, but just in case anyone else is wondering this as well, I have rolled the fender lip on mine with success. As you mentioned, there is that outer half of the wheel tub that is tac-welded to the fender lip. I cut that outer half wheel tub out which left me with the bolted on inner tub only. For the fender lip, I only rolled it so the inner lip was vertical because that made it flush with the fender as it curves up towards the top of the bed rail (in the cross section diagram, the dashed line is the outer fender well I removed and the arrow shows how much I rolled the fender lip in). If I rolled it in any more than that, I still wouldn't have gained any additional clearance because of the curvature of the fender. As for structural integrity, the inner bed wall/wheel tub is still plenty strong, but the bottom corners of the wheel opening are fairly flimsy without the outer wheel tub piece. These trucks did come with braces going to those points though, so as long as you put those back in the outer fender is still sturdy enough.
