If you do that, how are you going to get the count into the Pi? Remember, the serial input is already in use by the “emon” front end that gives you the analogue energy monitoring and the energy pulse input. This is why you need to use the Pi’s GPIO and a script or a service running in the Pi itself, passing the data to emonHub or emonCMS directly.
And this is what I had at the back of my mind that does just that, but didn’t find earlier:
Coming back to the original question, as your meter uses an active pull-down, you will need a pull-up resistor to the appropriate voltage to provide a solid logic ‘high’ to the input pin.
And the pinout: emonTx3 User Guide — OpenEnergyMonitor 0.0.1 documentation
You can of course parallel the one-wire temperature sensors, but you can’t do that with the pulse input, which is a logical voltage level input.