For the enchantment bonus, no it is not the same. I had a similar post a while back,
and it was pointed out to me that the MM2 Errattad it (i believe page 16 or so)
Adamantium gives a + to hit and damage, much like an enchantment bonus, but
will not overcome DR, and is thus less effective than an actual enchantment. It also
does not stack with an enchantment, meaning that a +2 enchanted adamantium longsword
would only be +2, but would retain the +2 to hit in magic dead areas( from the metal itself).