Actually, vertical spacers work just fine in Segment PRO as long as you are making a Feature Ring bowl as vertical spacers don't really belong in either painted segment or tornado bowls.
However, as pointed out in countless posts, Segment PRO is for making segmented bowls which fit in the 'standard' variety. Since the software is in charge of drawing the bowl for you, it simply has no idea what to do if the wall profile doesn't have enough data for it to understand what is required of it and what you are attempting to do is anything but standard.
However, it is a piece of cake in Woodturner PRO. Woodturner PRO does not know anything about standard turnings because you are always in charge. If you want to make a single row turning that has a single row that is 2" tall that has a 1/16" vertical spacer with six segments per row, change the thickness of the bottom disk to 0" and add a single row and set the parameters of that row however you wish. It will do exactly what you want and it will take all of about 60 seconds to do from start-to-finish. In fact, I've done it for you. I wasn't sure if you want to do it as a single row or a number of thin rows so I did it both ways and just added a blank space between them.
Yes sir, this does explain the reasoning behind limiting vertical spacers to the feature ring and in fact that does work as expected. Thank you for that.
As a suggestion (without the benefit of your explanation)... it might be less confusing to new users (such as myself) if the "Add Spacers" drop down in SegPro did not contain list item selections for Default and All Rings.