It sounds to me like you have inverted nipple - the condition that is, while not common per say, found often enough. The only problem you are likely to experience (if I am right with my diagnosis) is hardship while breastfeeding (if you do that one day) other than that, your nips are just as fit to play as any other!

Again, I can not stress enough - experiment and observe - make sure there is no excessive damage to the nipples after play (and if there is damage, give it time to heal and learn from it) and have fun. Usually if something does not feel right (and yeah, I know nipple clamps do not really feel right first few times lol) it most likely is not right. Every person is different from the pain tolerance level to preferences and reactions. Experiment and take it slowly.

P.S. if you should have big problem with the inverted nipples, there is simple surgical procedure that can correct it.

Hope this helps

red