No, you can't use Dual Weapon Attack after attacking with a (normal) two-handed weapon
Yes, you can use Dual Weapon Attack after attacking with the
stout end of a double weapon
From the Adventurer's Vault Errata (emphasis mine):
Stout: A weapon that has the stout property can be treated as a two-handed weapon.
Basically, whenever you want it to count as a two-handed weapon, it counts as a two-handed weapon. Obviously, you want it to count as a two-handed weapon for the purposes of the Power Attack feat but not for the purposes of the Dual Weapon Attack ability, so that's how it works. It isn't a two-handed weapon; you're still dual wielding for all intents and purposes, including triggering Dual Weapon Attack. But if you want an attack with the main-hand end to count as being made with a two-handed weapon, it does.
stout end of a double weapon is essentially a "two-handed" weapon that can be wielded in one hand, as long as you wield the other end in your other hand.