James,
OpenGL drawing is not exposed in the ArcGIS Explorer 900/1200 APIs - more info from SDK help below:
ArcGIS Explorer 500 exposed two events that enabled developers to draw graphics with OpenGL; this functionality is not supported in the ArcGIS Explorer 900 application; however ArcGIS Explorer 900 adds the concept of a Graphic, which is way to draw to the map using existing symbology�??graphics are not persisted to the map document and are ideal for drawing moving objects.
Regards
Mike