At runtime you may want to position UI elements, like buttons, text boxes, and select boxes. Since those don't exist in Spine, you could use placeholder images. At runtime you wouldn't need the images. You would just apply the animations and use the bone world transforms to position, rotate, and scale your UI elements.
If you are looking for something simpler, you could use the images at runtime and detect clicks on them. This won't behave quite like real buttons though, unless you swap out the images for hover and mouse down states. Even then you may be missing features such as UI element focus and keyboard navigation of the UI, but this may still be acceptable.