An overhand pitch with pure spiral spin is called a "cement mixer" and very often doesn't make it to the catcher. It certainly isn't a good slider. I think the confusion with spiral spin is well illustrated by this question though. A pitch with pure spiral spin (the dot made by spinning seams is directly pointed at the catcher's glove) doesn't move much at all regardless if it is baseball or softball. However, if you have spiral spin but the yaw is off center then there can be good movement. Even with that said, if the spiral spin pitch is consistently located and works then it doesn't matter what you name it