Ntop is run as a service via /etc/init.d/ntop, but it won't start up without being configured. If you invoke ntop directly, it'll do an initial setup guess and prompt you for an administrative user password.
Removing the line '--disable-schedyield' from /etc/ntop.conf was also necessary.
Errors and Resolutions
Dot Tool Not Found (encountered when hitting Traffic Map)
This is bundled with Graphviz. Go to Edit Preferences, then enter the key 'dot.key' and give it the path to the actual dot executable. Redhat uses /usr/bin/dot instead of the default /usr/local/bin/dot which Ntop expects to find.
Error 404 on Local Network Traffic Map
The directory /var/lib/ntop is created, with many files owned root:root. Doing chown -R ntop:ntop /var/lib/ntop will fix this.