Can the archiver exclude individual users from importing archived emails?

While our archiving appliance is not designed specifically for this, it can be done through the Exchange server.

If your organization is using an Exchange environment and running an enterprise solution, the Journaling service can be configured to prevent certain accounts from being archived. This service, which is responsible for capturing the emails sent to and from an account, can be set up to filter, on a granular level, through the mailboxes by security group or by email address, allowing web admins to exclude selected users or groups of users from the archival process, or from importing their historical data.