I have put rhinestones on a swim suit a couple of times but used fabric glue rather than heat setting the stones.
That was more because it was easier and faster than using the heat press.
If I had a cap press then like I do now I would have heat seat them.
These suits weren't meant to be worn except for the photo shoots they were done for so I don't know how well the glue from the stones would hold up a cholorinated pool.
Here's links to the two swim suits I've decorated with rhinestones.
Stitches Magazine - Feb. 2011 - Cover shot and article
Stitches Magazine - Sept/Oct 2011 - Bring on the Glam Article
Good luck with this and please post pictures. I would love to see what you do.