Yes, you can have the Dr CSS interface in the DR subnet of 6.2.1.128 and have the VIP address in the Main site subnet of 2.1.1.64

In 3550 does not support SIP Method in 12.4 T also.Cross-Platform Release Notes for Cisco IOS Release 12.4T, Part 2: Platform-Specific Information:http://www.cisco.com/en/US/products/ps6441/prod_release_note09186a00804a19a2.html

The following url will give you the details,http://www.cisco.com/en/US/products/ps6441/prod_release_note09186a00804a19ae.html#wp1698184

For interfaces that operate at 20,000,000 (20 million) bits per second or less, you must use 32-bit byte and packet counters. For interfaces that operate faster than 20 million bits per second, and slower than 650,000,000 bits per second, you must us...

RSPAN consists of at least one RSPAN source session, an RSPAN VLAN, and at least one RSPAN destination session. You separately configure RSPAN source sessions and RSPAN destination sessions on different network devices. To configure an RSPAN source s...