Hi mspope,
A short answer is, unfortunately, "no"- there are no currently supported Symantec products which protect Windows NT except Symantec Data Center Security: Server & Server Advanced. (This is the product formerly known as Symantec Critical Systems Protection, SCSP). If there is just one robot or gantry mill running WINNT I doubt this is what you are looking for to protect your company.
My SEP 12.1 clients are reporting RCP attacks,
Do you mean TCP attacks? What exact entries are appearing in the logs, and when did they begin? There are some instances where ARP events, etc are caused by the coding of the devices in a particular environment rather than an actual threat.
Troubleshooting Unsolicited Address Resolution Protocol (ARP) Requests
http://www.symantec.com/docs/TECH194746
Please do let me know if this is helpful!
Many thanks in advance,
Mick