This question has been answered by dvstudiosinc. See the first response.
The best way to do this is to create a postHook that sends a mail to your moderator email (you can define this in the postHook snippet), and then make the activationEmailTpl just contain a message to the user that their application is being reviewed (no link).
As for the postHook, look here for some ideas on setting it up (scroll to the examples): http://rtfm.modx.com/extras/revo/login/login.tutorials/login.using-pre-and-post-hooks