"Yes, it is acceptable. I was taught that it shows that you take the time to handstitch. Glue is risky and may not last as well as stitching. If you or a client are bothered by the visible stitching you can always put a liner in."
They're unique, under appreciated, and an art. I was lucky to study in London for millinery and continue since.
I studied at Western Michigan University for a B.S. for Textile and Apparel Design. My program took me to AIU, now Regent's University, in London where I had my first millinery course with Prudence, a wonderful instructor and mentor.
My first studio was in my small hometown of Pentwater, Michigan, USA. A lovely quaint resort village on the shore of Lake Michigan. I spent many nights creating and days managing a seasonal restaurant.
I now reside in Ann Arbor, Michigan and work as a Trim Engineer in the automotive industry. My studio is now a 'nook' in my apartment, smaller...but, great things are still being created.