yEd cannot parse SVG documents as graphs; i.e. yEd is not able to arrange visual elements inside an SVG document.
When you import an SVG document into yEd, the imported document can be used as an icon for a label or as the style/visualization for a single node.
If you want to use yEd to layout your data base schema diagrams, Oracle Data Modeler would need to offer an export into a graph exchange format like GraphML.
