I too am finding that the Category_Template field is not inherited by subcategories. (v3.0 & 3.01) dynamic.

I use category2.html for a series of categories and then revert back to category.html for the subcategories of these categories- deeper subcategories are still showing category2.html even though the field is blank within the record.

It worked OK in v2.x

I have already rebuilt the category tree and checked that the catroot and catdepth fields are set within the database.