I did a little test by exporting a single wall. The OBJ file has 6 g groups, as it should, because you want to be able to apply a texture to each "side". A single piece of wall is just like a box.

Adding an o object name changes nothing when importing into Blender, the same 6 object parts remain the same.

The only way to get a single object into Blender would be to merge all g groupings into a single g group. I haven't tested this but I suspect that you loose the separate textures.

From my point of view a single object in Blender is virtually useless, you want things to be as separated as possible because it allows you to manipulate them individually.