Prezado, precisei tb, peguei pelo campo ID da tabela ELE_USER. abaixo segue o método que utilizei, possa ser que lhe seja útil

function obterMatriculaLMS(loginFluig){
    if (loginFluig == null || loginFluig == undefined || loginFluig == ""){
        return "";
    }

    var comandoSQL = "SELECT ID " +
                     "  FROM ELE_USER " +
                     " WHERE USERNAME = '"+loginFluig+"'";
    //var dataSource = "/jdbc/FluigDS"; //
    var dataSource = "/jdbc/AppDS"; // Novo
    var conn = null;
    var stmt = null;
    var rs = null;
    var ic = new javax.naming.InitialContext();
    var ds = ic.lookup(dataSource);
    var created = false;
    try {
       conn = ds.getConnection();
       stmt = conn.createStatement();
       rs = stmt.executeQuery(comandoSQL);
       var columnCount = rs.getMetaData().getColumnCount();
       while (rs.next()) {
          var Arr = new Array();
          for(var i=1; i <= columnCount; i++) {
             var obj = rs.getObject(rs.getMetaData().getColumnName(i));
             if (null != obj){
                var valor = rs.getObject(rs.getMetaData().getColumnName(i)).toString();
                return valor;
             } // if
          } // for
       } // while
    }catch(e) {
        // silence
    }finally {
       try{
          if(rs != null) rs.close();
          if(stmt != null) stmt.close();   
          if(conn != null) conn.close();
       }catch(er){
           return "";
       } // try catch
    } // try finally
    return "";
}