The leaf/soil station's transmitter will not be received by your Vantage Vue. The Envoy would receive the signal directly from the leaf/soil station transmitter, though. Then the data will show in WeatherCat. The Leaf/Soil station varies how it can be setup, and the manual on Davis' site goes into detail on this.
The maximum that can be attached to a fully populated Leaf/Soil station transmitter is 2 leaf wetness sensors, 4 soil moisture sensors, and 4 soil temperature probes.
If you look in WeatherCat's Tools menu --> Live Data, you will see that Stu has allocated channels for up to 4 leaf wetness sensors, so you can actually use WeatherCat with more than one Leaf/Soil Station transmitter.
I hope that helps,
Steve