Questions about the isometric workflow

I was reading this article about Pillars of Eternity:

Backgrounds were rendered in Maya as a 2D image.
Is it possible to render an background outside of UE and import it in UE and use it as a level? If so, how to set up the lighting in UE for other 3D objects ?

I would like to start an isometric project and I wonder which workflow would be better: prerendered one or realtime and fully lit in UE?