I did not know they were illegal in CHSP. Second to last eBike demo I rode was through the backside of CHSP from Brush Canyon Park and exiting Bobcat/Camino d' Bryant. That ride, (And the day's earlier ride up Coal,) convinced me that as cool as eBikes are, they aren't for me. Pedal assist is nice, but trying to shove a 50 lb bike up Skully or Coal isn't fun even with a 250w advantage. I'll stick to the lighter non-assisted bikes.
As for OP's question, I'd be scared to take an eBike down San Juan given how bad most of them understeer.