The slot feature in Hole Wizard is a feature I was in favor of, and I do use it often, but it feels unfinished. I had suggested check boxes in the feature manager for "horizontal", "vertical", and "angled" (where the user could enter a value for the angle). As you know, it doesn't work this way. Instead it's placed with the line horizontal. That's fine, I guess, but it doesn't have a horizontal relation, so the sketch isn't fully defined, and the dimension usually covers the line so it isn't readily apparent that it's blue instead of black. I usually move the dimension and add the relation, but occasionally forget.
Last year I had a case where I edited something further up the tree, and when the model rebuilt the slots were at an angle. This is a great feature that wasn't well executed.