How to pass JsonObject from ArduinoJson to ESP8266WebServer object?
As far as I know, the only way is to serialize the JsonObject to a String:

String createJsonResponse() {
  StaticJsonBuffer&lt;500&gt; jsonBuffer;

  JsonObject &amp;root = jsonBuffer.createObject();
  JsonArray &amp;tempValues = root.createNestedArray("temperature");
  tempValues.add(t);
  JsonArray &amp;humiValues = root.createNestedArray("humidity");
  humiValues.add(h);
  JsonArray &amp;dewpValues = root.createNestedArray("dewpoint");
  dewpValues.add(pfDew);
  JsonArray &amp;EsPvValues = root.createNestedArray("systemv");
  EsPvValues.add(pfVcc / 1000, 3);

  String json;
  root.prettyPrintTo(json);
  return json;
}

void outputJson() {
    server.send(200, "text/json", createJsonResponse());
}


By the way, I recommend that you use the ArduinoJson Assistant to compute the size of the JsonBuffer.