udp broadcasts are sent to ALL computers on the LAN. That is why it is called a broadcast. You only need to make sure the other computer is listening on the correct port.
In eventghost, when you specify an IP address (in the broadcaster plugin settings) it is only the ip of the network card to listen on, in case you have more than one in your system. So if EVentGhost sends a broadcast on port 33000, all the computers listening on that port will receive it. the same is true for VoxCommando. If VoxCommando executes an EG action, all eventghost machines that are listening to port 33333 will receive the message.
I hope this answers your question, if I am misunderstanding you please let me know.
Edit: to be more clear, the IP address you set in the EventGhost broadcaster settings is not the IP of the machine you want to listen to. It is the IP of the machine you are currently running EventGhost on. If that machine has more than one network card installed, then it will have more than one IP and you will need to pick one to use as the listening device. Some people might have one network card connected to their LAN (so they should select that one) and another network card that is connected to the WAN ( a router / modem etc. )