I haven't really tested what happens if I make commits after the push. What I do know is that the rebase changes commit hashes. A push will put them on the remote repo, but the new hashes (and subsequently, new commits) are not shown in the activity stream.
In other words, a pushed rebase should force the activity stream to rescan the list of commits and add them to the activity list if they haven't already been added.
You will have to decide what the activity tab does with now-obsolete commits.