As is the case with all 3D effects in AE, the effect just creates a “live movie” that “plays” on a flat layer, which acts as a sort of movie screen. When you make the layer 3D, you’re just making the flat screen exist in 3D space, so if you want to flip the layer (screen) around, that’s cool, but the Shatter will still look like a movie playing on a screen.
As for the Shatter using the Comp Camera, that’s a trick that makes the “movie” look as if it is respecting the Comp Camera. Does that make sense?
Anyway, you need to make a 3D camera (if you haven’t already), then select “use comp camera” or such in the Shatter controls to make Shatter recognize the Comp Camera. Don’t make the Shatter layer 3D.
Steve