"does the NWN engine pick up if something is player made or an dropped item"
Nah, if resmelting is possible, its possible for all helms, armor, etc regardless of their origin.
Since you asked this particular specific question, you probably already know of the answer in the past that resmelting items that you've made won't be done, so... yeah, since they're indistinguishable, no resmelting of finished products
-TV