The license for the additions, at least for v4, is the GPL2. This was said in their IRC channel (not an official statement ofc), and I confirmed it by extracting the amd64-windows additions from the image and looking in license.rtf. That file lists only GPL2, but according to the official download site everything is also available as PUEL.
I can check further files on the image if you wish.
Would be really helpful if we can get an official statement about this.
Surely the license.rtf in the image is a legally binding statement?
That's for the GPL2. I don't think its relevant whether the PUEL is still allowed as a choice tbh.
It's GPL-2ized, you can see this here: http://www.virtualbox.org/wiki/Downloads
VirtualBox platform packages. The binaries are released under the terms of the GPL version 2.
VirtualBox 4.1.2 for Windows hosts x86/amd64
VirtualBox 4.1.2 for OS X hosts x86/amd64
VirtualBox 4.1.2 for Linux hosts
VirtualBox 4.1.2 for Solaris hosts x86/amd64
Please someone with access modify the PUEL license requeriment
+ 18 Jun 2013; Lars Wendler <email@example.com>
+ virtualbox-additions-4.1.24.ebuild, virtualbox-additions-4.1.26.ebuild,
+ virtualbox-additions-4.2.10.ebuild, virtualbox-additions-4.2.12.ebuild:
+ Fixed license as reported in the long overdue bug #365643 by Steffen