yepper. This way you model one single book and as long as they are the same width and height you can texture as many different covers as you like and stack as many of them as you like and twist them all any way you like. The renderer will handle not drawing the overlapping bits.

When they teach not to overlap textures they mean on a single object or within a single texture map. Your books are two separate objects that will just happen to be on top of each other in a scene. You can either create independent texture maps for each, put all the textures on a single map and just scale and move each books uv's or even create unique maps for each book outside the 0-1 space (this is a bit more advanced).