However you digitize your work to get it into the gallery, I think, is fine. Some people also take digital photographs of their prints that are too large to scan for the gallery.
You'll probably get a better result, though, if you have a macro lens or extension tubes for your DSLR, and photograph the slide using a tripod or copy stand and a light box.
If you have to photograph a projected image, then project small on a white sheet of paper and try to get the camera lens axis as close to the axis of the projector lens as you can.