i have been doing lots of blob-type environments in the last years for another engine and a typical setup was:
in maya:
choose a highres hdri in long-lat format (ideally aroung 16000x8000 pixels with a good dynamic range)
create a custom halfsphere with a floor
create a spherical projection in the center of the blob at the hight the hdri was taken
pin the uvs and tweak the blob…aka put the bottom edge to the bottom of a building and then go straight up to follow the vertical line of a building…to not get any bending effects from the spherical projection).
assign the huge hdri on a surfaceshader
cut the blop into: floor, top (make the cut at a hight that the top only contains sky elements, no buildings or trees) and 4x the sides
create a second uv set for all parts that is normalized into 01-space
bake the hdri into the 2nd uvset of all 6 parts…aka you now have 6 textures that fill the whole 01-space in 32bit with a resolution of 4096x4096. the top part can be usually lowered to 1024x1024 if the sky has only a gradient with not much detail that matters. you can convert the 32bit textures to 8bit since we dont plan to illuminate with this,…we just use it for the background.
copy your 2nd uv channel uvs to the 1st uv channel and delete the 2nd channel and assign your newly baked textures (the 8bit versions).
export your geometry to your engine and assign the textures to the emissive channel or whatever you have to do to make your geometry not receive any light.
for added detail around the center of the floor you can also split off the inner part of the circle and add a higher resolution to it with a seperate shader. then just add more detail to it with e.g. photoshop or mudbox. only this part can receive shadows (useful for car scenes with a hero object in the center of the blob.)
the illumination of the hero object was usually bakedin and the reflections come from a reflectionmap (aka a 32bit 2028x1024 version of the original 16k hdri)
im going to try if i can build this type of scene with UE4 over the weekend (only thing that seems to be a problem is the import of the 2k hdri for the reflections)