I would think there are an infinite number of ways to use Kuler in the creation of tees. Use or create color schemes you want to use in a shirt, and then copy the hex / CMYK values into your designer software, and arrange them how you like. Kuler is a great way to find working color schemes without sifting through loads of color books or randomly guessing what may or may not work.
Of course, the actual shirt color (the color of the cotton etc.) will probably be chosen for you by a distributer. Still Kuler can be of use from a 1 color to a 4 - color shirt, if you're trying to pick the right colors.