I’ve found a solution for this. It involves adding support for custom post types in the activity feed. As ‘forum’ is a custom post type you can add this (as well as other) post type’s updates to activity feeds.
The solution is over in the BuddyPress forums:
https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/display-custom-post-types-in-activity-feed/
The code that I got working is here:
http://pastebin.com/VJ6pR9az
Add ‘forum’ to the $media array to see sitewide forum activity. It only appears to work for content added after this is set up.
The version of the code at the bottom of this page:
https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/display-custom-post-types-in-activity-feed/
Is intriguing to me as it allows you to customize the phrasing of the activity notices, but I was unable to get it to work.
Awesome, updating my files following these instructions:
Login Integration Issues – bbpress and wordpress mu
corrected this as well as another issue I was having. Thanks!