I'm not a Poser user, so I'm not sure how Poser implements morphs, but generally morphs (aka relative vertex keys) rely on common vertex counts *and vertex order* to work.
If you simply bring a single OBJ, and not all the other morph targets, into Wings, and smooth it, you are altering both the vertex count and order... thus breaking the morphs.
If you simply bring a single OBJ, and not all the other morph targets, into Wings, and smooth it, you are altering both the vertex count and order... thus breaking the morphs.