The terrain would not be dynamic. Anything changing would be individual actors such as a flag that changes player colors when captured. Things like that.
I would probably make very large sections and snap them together, and place individual static mesh actors to fill it in. The terrain is structured with very specific boundaries like in starcraft; as opposed to something like Supreme Commander where units can more or less go anywhere you want.
Would Unreal allow me to paint directly onto the mesh like Substance 3D Painter does? I could see it being a big pain jumping back and forth because of rendering discrepancies between programs.