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:
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...