Hi,
Cisco WCS centrally manages all Cisco wireless LAN controllers including Cisco WiSM.
http://www.cisco.com/en/US/partner/products/ps6305/products_data_sheet0900aecd802570d0.html
The Cisco WiSM works in conjunction with Cisco lightweight AP, WCS and the Cisco Wireless Location Appliance to deliver a secure and unified wireless solution.
http://www.cisco.com/en/US/partner/products/hw/modules/ps2706/products_qanda_item0900aecd8036434e.shtml
You can have WiSM without WCS. But It will be a good package to have WCS to control all WLAN other devices, including WiSM. WCS is useful for planning, mapping, tracking, policy management, as well as wifi intrusion protection.
On the other hand, without WCS, you can maximize WiSM to provide full control, scalability, and reliability to build secure, enterprise-scale indoor and outdoor wireless networks, as well as to create and enforce policies that support business-critical applications.
Hope this helps.
Rgds,
AK