Do they actually play?
I can't comment on this particular project, but I know that similar projects have allowed adding images to the unused portions of the disc. A given region of the disc cannot be both image and data, but the disc can contain an inner region of data and imagery in the outer unused portion.
It supports putting data files either at the inner or outer rim, but it's at the cost of image space. So yes it can play, but not much storage.