Sorry for the delay in responding.
Yes, you can install CSA on an Exchange server, or on any server for that matter. CSA doesn't come with an Exchange server policy per se, but the standard default server policy will protect it from all known worms and viruses. CSA doesn't rely on signatures or updates in any way, it locks down a machine by looking for "malicious" activities and stopping them or alerting the user to them.
The following URL provides some doco on how CSA works to prevent attacks, particularly read the "Product Overview" chapter:
http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/cw2000/cw2000_b/vpnman/vms_2_2/csa_4_0/csa40usr/3957.pdf