Adding items to wooden_fences item tag via a datapack doesn't make them fuel. Other wooden tags (wooden_doors, logs, etc.) make everything in them fuel, including other items. 

Steps to reproduce:
-Add an item that can't be used as fuel to the wooden_fences item tag
-Try to use it as fuel
-Won't work
-Try the same item in the wooden_doors, logs, banners, etc. tags
-Will work as fuel