For a Buddypress installation of mine, I needed to add external rss feeds to groups. There is a great plugin for this work called BP External Group Blogs (http://wordpress.org/plugins/external-group-blogs/). Don’t let the name fool you, it supports RSS feed from every source, not just blogs. The plugin give group creators and administrators to attach external RSS feeds to groups. The posts appear within the activity stream for the group.
But I also needed a separate group tab to display those external posts (like the documents tab). So I made a simple extension plugin which does exactly that.
The plugin is called External Group RSS tab extension and you can downloaded from http://wordpress.org/plugins/external-group-rss-tab-extension/