Solved it! Amazing what lunch and a soda can do for your brain...
Anyway, in /root/ispconfig/scripts/shell the services_check.php script checks for localhost connectivity. That is what sends cron job emails. Changed it to point to the IP I have apache listening on and ran the script, no mail.
The script that controls the "services" tab in the web interface was also reporting it down, although that is the IP that I have "available" to host sites on elsewhere in the config. Assuming that it too was checking localhost, I simply re-edited my /etc/apache2/ports.conf file and have apache2 listening on the one IP and on localhost. No more red there either!