Check out the follow link from the ACE release notes.
http://www.cisco.com/en/US/docs/interfaces_modules/services_modules/ace/vA2_3_0/release/note/RACEA2_3_X.html#wp546319
Virtual Switching System Support
The ACE10 and the ACE20 running ACE software version A2(1.2) or later and installed in a Catalyst 6500 series switch running IOS software version 12.2(33)SXI or later support the Virtual Switching System (VSS). VSS is a system virtualization technology that allows the pooling of multiple Catalyst 6500 switches into a single virtual switch for increased operational efficiency by simplifying the network. Inter-chassis Supervisor switchover (SSO) boosts non-stop communication. For more information about VSS, see the Cisco IOS Version 12.2(33)SXI Configuration Guide.