Hey there! I'm not sure if you ever found a resolution. I couldn't get the Templates add-in to work but you can still get your template files that you made with a sort of work around. (Sorry if you already knew this, I wasn't sure if this might be helpful or not!)
- On your Home tab in Outlook, click New Items
- Click More Items
- Click Choose Form...
- On the top drop down, select User Templates in File System
There, you should be able to see your templates that you've made and you can select them from there! I know it isn't ideal, but I do hope this helps you or even someone else!