I posted a more detailed request here – https://gallery.menalto.com/node/74071 – I think the use of Gallery2’s multiroot + useralbum modules, with additional code added to the useralbum module to handle automatic creation of guest accounts with appropriate permissions for each useralbum, and code added to WPG2 to set the multiroot settings based on the current WP MU blog being viewed, may accomplish the goal of “isolated” Gallery2 views for each WordPress MU blog, while maintaining a single set of G2 tables and a single G2 codebase.
Hopefully a WPG2/Gallery2 developer can respond as to whether this is a reasonable way to accomplish the goal.
Thanks!