Configuring sudo to work without password
That should work fine assuming you put the %admin ALL=NOPASSWD: /usr/sbin/apache2ctl after the ALL rule and your goal is to have users of the admin group require a password for sudo for everything but the apache2ctl command.
What you probably want from what you said however is group of users that can start and stop apache, say apachestart. Then:
%apachestart ALL= NOPASSWD: /usr/sbin/apache2ctl
I think you might be able to make it truly everyone by replacing %apachestart with ALL, but I would recommend that even less.