It would a better idea to create a rule to allow the following website
http://liveupdate.symantecliveupdate.com
http://symantec.com
http://liveupdate.symantec.com
Say you have created a rule to allow X.X.X.X , Next time you run liveupdate, the request goes for y.y.y.y in that case the update would fail.
SO it is better to create a rule with the name, not with IP.