I believe they require a complete hysto to do a vaginectomy, but no, they don't just sew up the hole, and I doubt a regular gyno could/would do this. It really requires some knowlege and it has some risk from bleeding, which is why you want a very competent surgeon. Another reason why your run of the mill gyno wouldn't do this.
It is NOT a simple surgery. The usual surgery on trans guys involves taking the vaginal mucosa and sealing the walls, and then sewing the hole closed. It actually has a different name than vaginectomy.
--Jay