You obviously missed my comment re: the VirtualBox manual. The kernel module
must be loaded once it is compiled and installed or you are limited. You can
create VMs, but not run them. VMWare is the same.

Many times I have installed a new graphics driver and it tells me the
changes will take effect when I re-boot. Technically I do not HAVE to
re-boot, but then again I can't use what I want until I do. Since I need the
proprietary Nvidia driver for compositing then I cannot use Compiz until I
re-boot. The same can be said for installing a new kernel. It will advise
you to reboot, but you can still work if you want to.

As I see it my original comment re: Virtualbox stands and your correction
should be qualified to say that you don't have to re-boot but you can't boot
your VM until you re-boot your host machine on Linux. I can admit it if I am
wrong, but this is not one of those cases.