in JEM 2.3.+ there is the possibility to see these people,
but (because of a mistake) only when there is at least one person attending.
on the second tab in the JEM settings you can choose, who should be able to see that: nobody, only admin, every attending=registered user, everyone.
the second button is, if you can see not only attendings, but non-attendings/invited/waiting users.
The button for "admins only" doesn't work for groupmembers.