I'm not sure how you do it in Maya, but you're much better off rendering an alpha and compositing your background image later. It makes no sense tying a background image with the render. You might want to change it later, make small adjustments so it fits better with the render etc. You would have to rerender the whole image if you render them both at the same time.
In my opinion, It is the oposite.
It makes non sense to posprocessing if you can avoid it.
Pluss the interaction between the background image and the reflections in the objects, cannot be simulated in posprocessing, unless you invest days working on it and you are a genious on guessing reflections.