Unfortunately each OS has its own peculiarities. The message about needing Java 6 comes from the Mac OS itself, and it's a bogus message. This basic problem affects not just the installer application, but any other Eclipse application you will try to install using it, because the installer application is in fact just an Eclipse application and will suffer from all the same problems that it has. So yes, as far as I understand it, to run essay cheap or any Eclipse application on a Mac, you will need to install a JDK, best a JDK 8 at this point. Not that it's helpful to you, but for Windows, the installer is distributed as a native executable that does smarter checking of the available JREs and JDKs on the system so it does a better job detecting problems you will have when you actually try to launch the application, linking you to a page like this: http://download.eclipse.org/oomph/jre/?vm=2 filtered to the version that's needed when the right JRE/JDK is not available.

Certainly there isn't much useful to explain this Mac-specific peculiarity at https://wiki.eclipse.org/Eclipse/Installation nor in https://www.eclipse.org/downloads/eclipse-packages/?show_instructions=TRUE but I wonder if that's the documentation you think would be best to update, or were you looking elsewhere?