I'm not sure what your question is. If your topology is Internet[UTM][Switch]LAN, then the traffic between devices on the LAN doesn't pass through the UTM without some tricks that a technically-savvy person could easily get around.
I'm not sure what your question is. If your topology is Internet[UTM][Switch]LAN, then the traffic between devices on the LAN doesn't pass through the UTM without some tricks that a technically-savvy person could easily get around.