Using web_reg_save_param_xpath with DFES

Is it alloed to use web_reg_save_param_xpath with DFES; like in the example below

     web_reg_save_param_xpath(
        "ParamName=CatalogItemsName",
        "QueryString=//results/TranslatedTemplateName",
        "ReturnXML=No",
        "SelectAll=Yes",
        "DFES=JsonXml",
        SEARCH_FILTERS,
        "Scope=Body",
        LAST);

If yes has some one tried it? Is the XML generated by JasonXml stored somewhere?

Finally, can this function be with in web_concurrent_*