My VBA knowledge is Excel and not Word.

However, the Business Policy should include appropriate Templates for the various uses. Any document created should be created from that template. The Document used for a file will be listed in the documents Info. Any files that indicate an invalid or unapproved template would be subject to review automatically.
Users can add a Shortcut to the appropriate Network location of the Templates into the Personal Templates Folder.
A documents Styles in use can be viewed by Printing the Styles in Use for a document. In the Print dialogue from the File Ribbon, change the
Print All Pages to Styles. Obvious print to a PDF or other digital printer.
Style+ items will not be shown and would be problematic for this type of review.
Use the Document Protection feature with the Templates to restrict users to only use the Selected Styles. I believe you also want to restrict Style Set switching.