You can't add a generic material region to a style palette but you can add a custom backsplash.   The list of object types you can add does appear in the style palette specification dialog.  See picture below.  As you add things to the palette, they are removed from the Add Object list.   As far as adding cabinet partitions to the style palette is concerned, this is currently on our todo list but is just not something we have had a chance to get to yet.  Personally, I think w