What is the day today? Either I just don't know English well, or I get answers unconnected with each other all today's day. And about normals - theoretically, polygons can be without normals, but then the polygon doesn't be illuminated and viewport doesn't display that. However soft for polygonal modeling will see point…
You can render a polygon without normals. You just don't do a backface calculation. Or any kind of shading. But the precise answer would be that zbrush doesn't save normals as part of a file. It calculates them when it goes to draw a model. A lot of the things that apply to normal 3d programs don't apply in zbrush.