Shuyin and Tidus have a few similarities. Their looks being the most obvious ones but then there's also their absolutely identical fighting styles and the fact they both wanted to save a summoner they loved.
Shuyin of course went to more extreme lengths than Tidus.

Similarity 3 doesn't connect them in any specific way but 1 and 2, plus everything the game and Ultimania tells us, does connect them. It just seems Square finally realized people like to think for themselves and so they didn't do their best to destroy all speculation and independent thought.

Shuyin and Tidus' connection is up for us loyal fans to decide for ourselves.