I tried and was able to export them via folder...
first I made sub-folders in the root folder of the sprite
then exported them through SPINE > Texture Packer
then it exported what ever is within the assigned sub-folder into an atlas.
I don't know if it will be okay when placed in unity.... I tried playing with the txt atlas file.
- just about to watch video above now.
Finally watched the video.... I see. I don't have to meddle with the txt atlas files.
Thankies.