Hi,
As SIP (Session Initiation Protocol), is a signaling protocol for Internet conferencing, telephony, presence, events notification and instant messaging (as no doubt you are aware), this isn't supported in the normal Sniffer LAN products.
Sniffer does have a VoIP module called Sniffer Voice (latest version 2.1), and this does support SIP v2.0. I must admit I don't know the differences of the different SIP versions, and wether Sniffer Voice will definitely assist you. So it probably best to contact your local SE or support representive, and they should be able to help.
Alf