There are several remote agents available for Backup Exec. The most commonly used is the Agent for Windows servers. This is used for every backup of a Windows server, even the Backup Exec media server itself.
Remote agents for SQL, Exchange and other applications don't actually exist as standalone agents in their own right. When you install an application agent, you add the license to the media server, which unlocks the functionality of the agent. There is no extra software to install, or need to redeploy agents. The remote agents interact with the API provided by the application developer. This is why in some cases there are some configuration changes to be made to the application in order to allow Backup Exec to work correctly.
Obviously remote agents for other operating systems, such as Linux, UNIX and MacOS X are separate agents which require manual installation. The same is true of the agent for Windows NT4 for Backup Exec 11D. These additional agents can be downloaded from Symantec Fileconnect.