Well, I can explain how to use UVMapper for this but I don't know that it's going to work in your case - nor do I think any morphs will either if you're altering the geometry (subdividing alters the vertex count). It has been awhile though.

For the UVMapper trick, you usually want to save a copy of the original obj you're working from, that way you have access to the previous grouping.  A simple copy and paste to a new location would suffice but you could also load the obj into Uvmapper and save to a different name. Then you do what you need to do in ZBrush and if it destroys the group names, you simply import the untouched obj's UV's. It will automatically reassign the grouping/materials as long as no changes were made to the vertex count. The idea is, since the geometry is the same order/number of verts, copying between a morph and the original won't cause problems.

Subdividing introduces new polys into the model though and that changes the vertex count, so if you save a subdivided copy of the model, you're gonna have a hard time. You'll likely have to manually rename the groups and probably kiss the pre-existing morphs good bye.