I don't see any well trained tailor makes dummy suit for fitting, it is not necessary and not helpful. When dummy suit is made, no basting thread is used and the fitter can't remove it for pinning (think about the shoulder seam and armhole seam).
However, some may baste muslin to do fitting before cutting the real fabrics, esp for 1st time client.
I believe they got a good base pattern (surprisingly, they use CAD for pattern making). But I don't know how well they do for fitting, they just make me feel like amateur ..... So, whenever the client with disproportionate figure, that may make a big trouble ...
Speaking of the buttonhole, they use a grimp thread (probably gutermann agreman #1) to support the buttonhole stitching and so you will see it is not flat. You can just buy it and ask your tailor to use it when stitching the buttonbole.
Where can I buy grimp thread in Hong Kong ?