Reference the supported devices tables for LMS 3.1: http://www.cisco.com/en/US/docs/net_mgmt/ciscoworks_lan_management_solution/3.1/device_support/table/lms31sdt.html
If your FWSM reports as snmp OID 1.3.6.1.4.1.9.1.674 (which it probably does - as does the FWSM in a 65xx chassis), it is supported by the RME component of CiscoWorks only.
In general, all the Cisco firewalls have limited CiscoWorks functionality/support. See the following FAQ section for FWSM management options: http://www.cisco.com/en/US/customer/products/hw/modules/ps2706/products_qanda_item09186a00801e9e26.shtml#q6 Note that, in addition to the tools cited in that document, ASDM can also be used to manage a given firewall.
The same table I cited above notes that the SAMI (assuming it's OID 1.3.6.1.4.1.9.1.744) is supported across the CiscoWorks LMS applications.
One can use snmpwalk to ascertain a given device's OID.