Matt, I think this would not be good, you often need different postprocessing in different views. That would not work with postprocessing the whole frame buffer. Its better to postprocess views separately.

Grafton, Petra is right, your invisible view ent was just a clear mistake in your code. Thats what people tried to tell you all the time, you still seem not to understand.

You must not render them into the camera target bmap. You must render them with a normal view on the screen. Thats just missing in your code. When you dont assign a normal view, the entity uses the camera view by default and then you cant see it because of your code. Its this simple, no new engine feature required here.

I have lens flares together with a HDR shader that I took from a shader lib, I believe it was shade-C. Its using many render targets and I also never had a problem with my view ents.