You may be right about his name being Hiroshi and not Hiroyuki. If there is a website of which I trust the most is MPN (Music People's Nest), I haven't found a single incorrect reading of the musicians' names registered in their database, and in this
page and this
other one his name is given as "ミナミ ヒロシ" (Hiroshi Minami). Nevertheless, I have found no mention of "Hiroshi Minami Group" that should be the correct name of his group of horn players.
It's a difficult case, because there are many credits pointing in both directions.