I'm totally new to modelling applications. I have the trial version of 3D Coat. I have a Full body obj that I exported from Poser 2012. I want to smooth parts on the mesh in 3dc. I import the obj into 3dc using the 'Reference Mesh' option.

Here is the problem. When I apply the smoothing brush, the mesh tears apart at the group boundaries. Even it I use UV Mapper to assign all the mesh to one group, it still tears apart where the boundaries used to be. Presumably this is because those facets are not welded. If I weld the mesh, I can smooth it in 3dc, but it will no longer function as a morph in Poser.

Is there a way I can use 3dc to smooth the mesh, and still be able to use the result as a morph in Poser?

If "smoothing" the mesh does anything other than move vertices around or calculate a set of normals (which Poser will ignore) then you won't get a morph from the result.

I suspect that "smoothing" in this case means subdividing the mesh, which like any other operation that changes the number of vertices is forbidden for morph making purposes.

No, Smoothing is smoothing. It averages the distance between vertices on the mesh - as in ZBrush or Mudbox, etc.  it doesn't add any additional geometry as subdivding would.

Les, I don't know what figure you're doing this with but you should try using the OBJ from the Runtime and NOT an exported obj.  While the majority of Poser figures are not welded, many of the figures from Smith Micro are. You can load an OBJ of Miki3 for example directly from your Runtime and it should stay solid as you apply your smooth brush. It should even stay welded as you subdivide (if you need to for some reason).  For models with breaks  in the base OBJ, you'll need something like Poser Morph Loader from Colorcurvature for now.