I started researching this story a few years ago for my website, then started again this spring when I was writing my book. Unfortunately I only got as far as a couple newspaper articles that all seem to be from the same source.
The Cuban Giants were a top-notch traveling blackball team at the time and fairly well covered in newspapers. When the Cuban Giants came to town it was a big deal back then and the added attraction of a Japanese ballplayer would have certainly turned heads and left a trail of newsprint. Since there weren't many Japanese ballplayers in the U.S. in 1905 it would seem that his story would have been fairly easy to research, but I came up with zip.
It seems others have also found this story intriguing and have not found anything else substantial on it. Here is a link to a blog about two researchers trying to find out about
Sugimoto.
I hope someone can find something on this guy, it's a neat story, but part of me thinks it was McGraw pulling a sports writer's leg, or a bored scribe having fun. It kind of reminded me of an 1887 newspaper article about the White Sox signing a Chinese pitcher named
Teang Wong Fu.