How to wrap a DMG file with a wizard installer?
It's not perfect, but I've got something very nice by using a combination of IzPack and https://github.com/Jorl17/jar2app

The IzPack builds a java installer but then you are stuck with an executable jar file. That's where jar2app comes in - you can convert the jar to an app file with a bundled JRE. 

Works for me, not perfect because the installer size gets kinda bloated. And also now you have a .app file which is actually an exploded archive. So you have to wrap that in a DMG. But that works.