This is working as designed. The install applies required registry keys. They are found at:
HKLM\Software\Altiris\CredentialManager\Keys
HKLM\Software\Altiris\eXpress\Altiris_CredentialManager_Agent\version
If it is suspected the agent wasn't properly installed, check these two locations to confirm the install executed successfully.
This install will not register a plug-in shown in the Symantec Management Agent's UI or in the agents table in the database.