FaceGen works best with two photos (front and side). If you use only one photo, the side profile will look like a generic average. For Genesis 9's realistic profiles (which have distinct jawlines from Genesis 8), using one photo results in a "morph clash." Always use two photos.
Historically, Daz artists used a product called (by Raccoon or similar developers). This tool acted as a bridge: it mapped the FaceGen shape onto the Genesis 8 base using a proprietary morph. facegen for genesis 9