if($Server::Dedicated)
//Server is dedicated
From that, then:
if(($Server::Dedicated && %client.bl_id $= getNumKeyID()) || %client.getRawIP() $= "local")
//%client is the server host
EDIT: Actually, I just checked, getNumKeyID() seems to work on a client copy as well, so just use what Ephialtes had:
if(%client.bl_id $= getNumKeyID())
//%client is the server host