So the DZ Shuyin is never explicitly mentioned, but a logical conclusion to events established elsewhere in the games. So by extension there's also a DZ Lenne that DZ Shuyin presumably lived with happily, unaware that their real life templates died in misery.

Externally the resemblance between Tidus and Shuyin drives the plot; if Shuyin had looked like anyone else, there would be no X-2. But internally to the plot it raises a lot of issues that the game avoids addressing.