http://docs.daz3d.com/doku.php/public/dson_spec/start

This format is not intended to be fully backward compatible with Poser content, although extensive efforts have been made to accommodate features of the Poser file format for features that are common to Poser and DAZ Studio.

Ok - from the Keyboard of DAZ to your eyes. Enough about DSON already. It's old.

Which is stating that Poser Content, such as Victoria 4, is not fully compatible with the format. It is not stating that Poser could not import the format, or that Content in that format could not be used in Poser, given the DSON importer for Poser or Poser adding a native importer.