I'm looking this up currently as well. Someone on another board said this command is the one to use:
"set-VMSwitch -Name "Your Network Team" -AllowManagementOS:$false"
I haven't tried it yet, but I figure this seems like how you'd do it. I'm currently searching to find out best practice for SET teams, for all I know you aren't supposed to exclude the management OS from SET teams (not that that would be reasonable). :)