Publish Wordpress login, in both Wordpress or WPMU, can one alter the link to in which the user lands. Example: Once user has drenched into Wordpress, I would like these to be forwarded to the landing index.php from the primary website (webpage) rather than the consumer Dashboard.

This Wordpress wordpress plugin appears to complete exactly the thing you need. Unsure about WPMU but you may can leverage the functionality:

Best of luck!