Making a DMG is fairly easy using hdiutil on OS X, but let's not forget that OS X isn't everybody's system -- we see a lot of Linux and even Windows at hackathons.

I would recommend building ZIP archives for Windows and Linux and tossing them all on the same target USB stick. Mac-specific things might be safer in a DMG wrapper (especially if we bundle VirtualBox etc).

With the advent of the cross platform ISO image, I don't think this is actually worth investing energy into. One problem that would be fundamental here is that the WMF doesn't have servers that could be used to automate OS X build steps.