Duke Snider did not start the game in question.
He was sent back to the minors in July then recalled in September. He was not eligible to play in the 47 series. He became a starting outfielder for the Dodgers in 1949.

We still need the pitcher. I go with Branca.

Dodger outfielders in 1947 were:
Reiser, Hermanski, Furillo and Dixie Walker. Could have been any combination of the 3.

No matter who played, Robinson's 1st day at the park is still one on the biggest milestones in Baseball history. The fact that Duke is in the picture was pure luck.