Wow, I've never compiled my own Apache, nor has anybody I've worked with ever suggested we do so. I suppose I can imagine going to the trouble to do so in some situations, but there are a _lot_ of advantages to using the vendor packages.
That said, configuring two apache instances (one backend and one frontend) using stock Ubuntu apache is not terribly hard. I use the vendor-supplied config dir for the frontend, and set up a parallel directory structure for the backend (/etc/apache2-backend, /var/log/apache2-backend, etc). Works great.