Yes, but largely by a Japanese team moved over out of hopes they could train the Americans and corporate politics.
And I believe Tommy Tallarico was the first American to work on the Sonic franchise, ever.
Still? Pretty sure it's widely acknowledged as one of his many fabrications.
He absolutely was not. The first Sonic game involving American developers was Sonic 2 on Genesis (developed at Sega Technical Institute with a combined American and Japanese crew), and he did not work on that game.