Will putting an e-bike chain on a "traditional" road bike give more mileage?
Chains don't stretch under any kind of normal use, even the kind of power that an e-bike can put out (which, to be fair, can be several multiples of what a fairly strong rider can put out for extended periods). 

Chains elongate through wear: the combination of lube and environmental grit acts as a grinding paste between the moving parts of the chain, so that side-plate openings enlarge (or rivets wear down), resulting in a longer chain overall.

If you want your chain to last longer, keep it clean.