Surely it's not suicide. In Islam our intention and our tries are what we decide and the result is decided by Allah. So if you intend to dive and die it counts as suicide, but if you know the risk and dive for fun and adventure then it is not.
Everything has a risk but the percentage is just different; in an air plane you have safety in 99% of flights; in car driving in an European country you have 2% risk of crash; in 3rd world countries you have 30%. SoSo even if the risk of your life is 99.99% but your intentions are to survive even with 0.01% probability it will not be counted as a suicide.