I had a similar issue where I would try to call reverse('admin_index') and was constantly getting django.core.urlresolvers.NoReverseMatch errors.
Turns out I had the old format admin urls in my urls.py file.
I had this in my urlpatterns:
(r'^admin/(.*)', admin.site.root),
which gets the admin screens working but is the deprecated way of doing it. I needed to change it to this:
(r'^admin/', include(admin.site.urls) ),
Once I did that, all the goodness that was promised in the Reversing Admin URLs docs started working.