BuddyPress.org

For future reference, I figured out how to do this: I’m using the plugin

https://buddypress.org/forums/topic/groupblog-v13-adding-members-instantly-thanks-boone

So long as people join the group associated with the main site, they’re able to add blogs to the site. I make everyone a contributor so their blogs aren’t published automatically and I can then add them to the category – Member Blogs.