OK this may be obvious but have you actually tried using useradd to create an account before running your ausearch?

From: linux-audit-bounces@redhat.com [mailto:linux-audit-bounces@redhat.com] On Behalf Of Alarie, Maxime
Sent: Monday, July 06, 2015 10:03 AM
To: linux-audit@redhat.com
Subject: EXT :How to make sure a specific event is logged with thge proper message type?

Hi,

I have this rule in audit.rules : -w /usr/sbin/useradd -p x -k user_modification

When I add a user, and do a ausearch –m ADD_USER   I get 0 match.  Am I doing something wrong here?  I am using version 1.8.

Thanks