vmware - Can a hypervisor like VirtualBox be used to launch a virtualized OS which is also directly bootable?

This question is rather theoretical:

Suppose I have a PC with two different OS on two different partitions: OS1 on sda1 and OS2 on sda2. Is it somehow possible to set up a program like VMWare or Virtualbox in OS1, which accesses sda2, boots it and runs OS2? On the other hand OS2 should be bootable directly, as well.

I realize that the emulated OS2 would be an awful lot slower and probably noone would really use this setup, but I find this very interesting.