I’m using a similar approach (with skeletal mesh components) but instead of slicing the character up into several body parts every of my character components represents a different type/layer of clothing like underwear top, underwear bottom, shoes etc.
I tried to play with the hd mesh in blender but somehow it lacks the vertex weights and I don’t see any way of transferring them from the ld to the hd mesh. The documentation says nothing about the right workflow of importing hd characters into blender.
Apart from that: Any news on the shadow issue?