^^^ I think the rad support was mentioned, not the rad. But, indeed, an AL rad is best not grounded to lower electrolytic action. Notice that production AL rads use plastic tanks and plastic/rubber supports; the AL rad doesn't touch the chassis.
Just another reason to keep one's coolant regularly changed out: keep the anti-corrosion additives fresh to give any hard mounted AL rad as much help as possible.
The multiple epoxy paint coats is a good reason for the extra grounding setup; an interesting problem.