The install on OS X 10.11 appears to go fine. At the end, I get a popup saying "Server was replaced in the Applications folder". However, when I go to launch Server from my applications folder, it launches Server version 4.1.51.
Best I've found in the release notes is this:
Older versions of OS X Server can launch on OS X v10.11 Developer Beta 1 after an OS upgrade or migration. Quit OS X Server and install OS X Server 5.0 Beta 1.
... but this is immediately after the 5.0 Beta 1 install, not an OS upgrade or migration.
Is there another way to launch Server 5.0 beta 1?