I could get an imported background to render with the image (GPU) but could not get the render dimensions to match the background image. I've never used render over background in that way so I'm probably the wrong guy to ask. What I do is load an HDRI onto the background in the mat room and use it as the lighting for the scene. Make sure you make the construct invisible in your hierarchy.

W10, Ryzen 5 1600x, 16Gb,RTX2060Super+GTX980, PP11, 11.3.740