I noticed this the other day when me and my mate tried this combination out.
They can pretty much outzone any combination of character with a combination of spam grenades, rockets and sniping.
Emmett always has cover with which to gather ammo and the AP generator lets them both enjoy incredibly fast AP gain while keeping enemies at max distance. On hades stage they are godlike together.
Anyone else given this a try?
You would have thought emmett and emmett might work but you just end up destroying each others equipment.