Well, if this thread has already been resurrected...
I eventually solved the problem by creating an item link for a stat-less item with the given enchant ID and parsing its tooltip, and would like to thank the author of
this add-on for the idea (and most of the implementation).
As for shamans, I used
GetWeaponEnchantInfo to see if a weapon enchant exists, but this indeed does not tell me what the enchant is.