Hi emregoren,
To my knowledge, the Camera Shader has never worked in the Picture Viewer (I checked a few versions today) while using any kind of preview renderer, like the Viewport Renderer. In the earlier versions of Cinema 4D, the Camera Shader showed black, now in newer versions, it is green.
When you render to the picture viewer, the interactivity with your scene stops, of course. This means, if the Camera Shader is set up correctly, you could “Bake” the animation and use the result of the baking in a different shader to have all parts in the way you need it. This baking doesn’t show viewports elements. You haven’t mentioned why this needs to be in the Picture-Viewer and no reason why the editor (viewport) is not sufficient.
In case I miss something here, you might check with the tech support.
https://support.maxon.net/index.php
All the best