correction, just checked... the material lines within the object file start after the vertex normal (vn) lines at the head of the face definitions and continue as group per material within these definitions (easiest way would be a find 'usemtl "name"' with the text editor).

Also, just to double check opened an .obj file in a text editor, deleted the material definitions and loaded the associated .cr2. The result was that the material names were still present within the material room but since these materials were no longer associated with faces of the geometry were rendered functionless... Essentially phantom debris loaded from the .cr2. Conversely I did the same process with the .cr2 file and when the figure was loaded in Poser, as earlier stated, the material regions and their functionality were still intact but the material qualities were no longer intact.

The only sure way to completely delete unwanted material regions and the corresponding material names within a figure via text editing is to edit both files. Be careful within the .cr2 to leave the preview material intact and to only delete the usemtl 'name' line within the object. Don't delete the G line and the group assignations (numbered f lines) or you'll lose your groupings.