In most cases, no. The faint odour that may come from the urine hose is drawn out through the vent pipe due to the action of the fan. A water seal is only needed if a strong odour from the greywater system would be noticed inside or outside the house.
If needed, we sell a Separett in-line trap for the urine pipe.
If you are using standard rigid pipework, look at products such as the HepVO inline trap.