CSC-SSM module is used on ASA to scan the network traffic for HTTP, HTTPS,SMTP, POP3, FTP aprat from that it does not scan aly other traffic.
I am not 100% sure of what you asked but CSC-SSM does not have a sublet of its own neither it acts as a L3 device
The IP address that you assign to the CSC-SSM is only to manage it and also for DNS query as it needs to resolve FQDN names for the HTTP traffic through configured DNS servers; not used for routing purpose.
Please refer to the following latest configuration guide to understand better
http://www.cisco.com/en/US/docs/security/csc/csc66/administration/guide/csc1.html
Regards,
Sachin