IIRC, even though ISPConfig allows you to put in multiple IPs it actually doesn't have communication or support for multiple servers, right? Will I have to maintain two different ISPConfig setups of all the websites? (Drupal multisites with a bunch of sites on 1 IP using Named-Based Virtual hosting using howtoforge setups)
You should be aware that you try to setup a ultiserver system with a ispconfig version for single servers. ISPConfig 2 is a controlpanel to be used on single servers, so it has no functions to help you to run it on multiple servers at the same time. For multiservers etups, there is ISPConfig 3 available which supports the configuration mirroring out of the box over two or more servers.