DT deployed FX applets are deployed as the following code snippet does:
==========Begin of Code===============
function embedAplication() {
        dtjava.embed(
            {
                id : 'sampleApp',
                url : 'EvalTest.jnlp',
                placeholder : 'appletplaceholder',
                width : 300,
                height : 300,
                params : {"eval_string": "1.1 + 1.1", "expected_value": "2.2", "expected_type": "java.lang.Double"}
            },
            {
                javafx : '2.0+'
            },
            {}
        );
    }
==========End of Code===============

Seems Relative Dimension does NOT work with DT. If we specify width and height as say 50%, the applet won't be loaded.

Try access http://sqeweb.us.oracle.com/net/sqenfs-1/export1/comp/jsn/users/stephen/deployment_stuff/sqe_ws/7/deployment/src/javafx/LiveConnect/LiveConnect/html/RelativeDMWithDT.html in browser, if the applet won't be loaded, then the issue is reproduce.

Non-Relative DM applet works OK: http://sqeweb.us.oracle.com/net/sqenfs-1/export1/comp/jsn/users/stephen/deployment_stuff/sqe_ws/7/deployment/src/javafx/LiveConnect/LiveConnect/html/NoRelativeDMWithDT.html