I'd recommend going with option 1 - keep sub-category unique within category. Let's say I have two categories of unrelated items:
For each I want a subcategory
Notice that Orange is a sub-category within each category. Although the name is the same, it's function is very different. (Let's not get into the possibility that Orange fruit is orange in color)
With this design, if someone changes their mind and wants to rename Orange to Oranges, fine. It's easy to change without affecting Orange sub-category under Colors.
If your UI is built in such a way that Marketing can control subcategories of Colors whereas Production can control subcategories of Fruits, this design will allow Marketing to work with their subcategories without stepping over Production's subcategories.
