Hi, I work with polymer clay all the time. I often bake holeless glass beads in for texture and also attach findings and beads as part of a design. Since the clay is fired at such a low temperature, I've never had a problem. I would be concerned if the things you are incorporating are large, like those glass pieces used in vases but as for seed beads, as long as they are color fast, you shouldn't have a problem.
Do as they advise anyone trying something new: do a test piece and see how it goes. You can also lower the baking temp recommended on the clay by 10 degrees but then bake it longer. If the beads you are incorporating "pop out" after baking, you can secure them with a tiny drop of any glue compatible with pc --- just make sure it's the dry clear variety.
Probably more than you wanted to know but hope it helps.
Barbara