This is on Windows 8 x64 Professional, NIS 2013 V20.2.1.22, and MS Office 2013 Home and Professional 2013 (32-bit).
On removing Office 2010 and installing the local version of MS Office 2013 Home and Professional (32-bit), Outlook 2013 does not show up in Client Integration of NIS 2013 (Settings>Network>Message Protection>AntiSpam>Client Integration. Is NIS 2013 not capable of supporting Outlook 2013?
Sorry for the post. I found the answer here: