This works as designed in MNE. Outlook stationery does not work exactly the same as Notes.
In Outlook, stationery is stored on the end user machine, not the Exchange server.
In Notes, stationary is stored in the Domino server. MNE migrates stationery to Exchange as a folder.
it will not migrate it to every end user's machine which Outlook can apply it.
The end users have to save the stationery in their Outlook, then they can use it as a template.
See how to save mail as stationery details here:
1. if there is no stationery folder under %appdata%/microsoft, you should create it firstly
2. if there is no HTML type selection, you can save as RTF firstly, then change the file extension manually.