Alex Narvey at Precursor Systems noticed that OS X Server 5 makes changes in the way in which you can implement reverse proxies.
He has been using reverse proxies under OS X Server as a means of running FileMaker Server, Kerio Connect, and Rumpus alongside regular Server features such as the Web, Wiki, and Profile Manager services. Normally this would not be possible on a single server, because the Server app runs its own instance of Apache.
He has generously provided a tutorial covering how to configure a Mac server so that these can co-exist, and so that future updates will be manageable, using reverse proxies. You can obtain this from Precursor’s site: it is listed in the tutorials section at the foot of this page.