Using the attached mission, export it onto a server, have yourself and the HC join onto the two slots, wait 5 seconds after missions start and then check the RPT log for the server, your client and the HC.
On all machines, the following messages will be logged in the RPT, except for the HC:
"BIS_fnc_MP Test log"
"BIS_fnc_MP Test log"
"BIS_fnc_MP Test log"
"BIS_fnc_MP Test log"
"BIS_fnc_MP Test log"
These messages where created by the BIS_fnc_MP only being run on the server with the following command:
[[[],"log.sqf"],"BIS_fnc_execVM"] spawn BIS_fnc_MP;
Where log.sqf contains:
diag_log "BIS_fnc_MP Test log";
5x.