Are you asking if yEd has an integrated editor for creating SVG documents or raster images that may be used as symbols for nodes?
No, such an editor is not available in yEd.
Given the fact that there are very sophisticated SVG editor applications (e.g. Inkscape) and lots of image editor applications (e.g. the GIMP, MS Paint, ...) available for free, you are most certainly better of using one of those dedicated applications than anything built-in to yEd for creating custom symbols.
Nevertheless, it is also possible to create "new symbols" in yEd through creative use of labels and yEd's support for converting nodes into labels. (The latter may be achived by moving one node over another, right-clicking the moved node to open its context menu, and choosing "Convert to Label".)
See e.g. "Help" -> "Example Graphs" -> "Visual Features" -> "node_labels_with_icons.graphmlz" for sample visualizations created with the help of multiple labels.
