Part of the problem is that the word "group" has two different meanings
inside Poser and many more meanings outside of Poser.

In the OBJ file, verts are numbered straight through from start
to finish, and the numbering crosses Group boundaries without
any pauses.  But in Poser, some of those Groups end up being
body parts and some may only become material zones.  For the
sake of morphs, Poser numbers verts by body part, so the 
numbering in the original OBJ won't match at all. 

In your example, the Head has 10 verts and you want to morph only the
verts numbered 012789.   It doesn't matter if the head contains Groups
that are actually material zones.  You'd still export the entire head as 
one OBJ, then use the modelling app to move those verts around, then 
save the result as an OBJ.  You'd then load the full figure in Poser,
select the Head, and add this new OBJ as a morph.  All the verts
of the Head must be listed in this new OBJ, whether you changed
them or not.  (In other words, this OBJ is a complete Head with a
different shape; it's not just the changed points.)

The vert numbers in this morph-target OBJ will then be the same as the
original Head ... provided you haven't done anything like smoothing 
that adds or subtracts verts.   (You probably know about that limitation.)  

Groups for material purposes shouldn't affect anything, because they 
are not separate body parts.   If the Lip was listed by Poser as a separate 
body part, then you'd have to exclude it from the export to begin with.

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