If this exists, I have no clue where to find it. My asking around has gotten nowhere as well.
GetEquipType() covers armor well enough, but I wish there was a GetWeaponType() to return this set of globals about weapons:
http://wiki.esoui.com/Globals#WeaponType
*edit: I figured that while I'm here, I'll extend this quest to GetArmorType() too; we need a way to get heavy, medium or light without having to resort to fallible icon parsing.