Nope. The book says enhancement bonus, not magical enhancement bonus.
But since the weapon comes out more expensive, not less expensive, there's not really a problem with it. (unless you're one of those people who also think that spending an extra 1000gp on a weapon/armour which cannot sunder or penetrate DR is such a fantastic deal they just have to rule against it).
With all the things adamantine CAN'T do, it's a wonder it's even in the rule book (unless when they wrote it, they were already planning for forsakers...)