Quote - I guess all DSON V6 comes with ?
1 DSON Core Installer
1 Poser Companion Files Installer

Will how well DSON works depend on the what Artist made them ?

Does DAZ require all venders to include DSON ?

DSON is the scene file notification specification that is saved from DAZ studio. So scenes, materials, characters, morphs, etc are saved in DS to this spec. So everything that is saved in DS is DSON. This is not a import technology though, and I think that's what confuses everyone.   Poser reads the DSON specification through the DSON Importer. The importer is the technology, that reads the DSON specifcation just like DS can read basic mc6 files from its built in importer.

So everything that is made for genesis is not automatically Poser ready. Clothing and certain morphs have to be made a certain way and tested in Poser to make sure it works, and from that a vendor would create the Poser companion files. So if you see a product that includes companion files then it was tested for use in Poser.  If those files aren't included, you can try to make your own companion files or use one of Mec4D's or Dimension3D's utilities to read the files, but it may not be guaranteed to work. For example DS does not require clothing to be grouped so those will not work in Poser, but works fine in DS. Also clothing that uses smoothing in DS will have issues in Poser as well.

DAZ does not require vendors to make items that are compatible with the DSON importer for Poser, but there are a few vendors such as FWArt, OOT and Nikisatez, that use Poser for their rendering so they include the Poser companion files for their characters and clothing. Also my products include companion files and include custom adjusted rigs so the scaled characters (such as the hero shape and the teens) work in Poser as well.