This can be done with a sql query. If you are comfortable with running queries, go to your phpmyadmin, choose the database that you used for installing your forum and run this query in the SQL box.
Code:
SELECT style.title AS 'Style', user.username AS 'User'
FROM `xf_style` AS style
LEFT JOIN xf_user AS user ON
(style.style_id = user.user_id)
ORDER BY style.style_id;
This will list all styles and members using them.