I can understand your confusion. That doc is in the consumer database and is, I believe, referring to the consumer product (the Norton at the top, the "num.nsf" in the URL). It hasn't been updated since 2005. Our enterprise AV for Mac documentation has been moved to the Enterprise Security KB ("ent-security.nsf" in a given URL).
This is what I found: the Server OS has not been extensively tested with the AV client, so is in that sense unsupported. However, since the server is essentially the client + added server features, I personally would not have an issue assisting a customer with an AV client issue on a Mac server OS. Our own Mac server in our Mac lab runs it with no problem. (To be honest, I can't actually recall a case I have ever had with AV issues on a server OS.)
I did not see any specific information in the
System Requirements for SEP document regarding the Mac client. I will see about that.
sandra