As far as the Leonardo and the reset capability, this is (I believe) what the DTR pin is used for in Unos
The UNOs don't have a DTR pin but the ATmega16U2 has a GPIO that is used to reset the ATmega328P. The DTR pin on the XBee is used only for having handshake lines for firmware updates. Where in the documentation have you found that this signal is transmitted to the remote XBee in a standard serial configuration? To my knowledge this is not the case. It's something different if you load your own firmware on the XBees, then you can use any of the GPIOs and connect it to the reset pin of the UNO or Leonardo to reset the Arduino. But you also have to take care that the reset line of the Arduino is NOT connected to the reset line of the XBee (which usually is the case) because else you won't get in a communication state fast enough before the bootloader finishes waiting for a new sketch upload.