Does this work? Yes it does currently. With OpenBSD 5.0, 5.1 an VirtualBox 3.2.
Without hardware virtualization on my CPU I had to start VirtualBox differently than normally, though:
VBoxSDL –norawr0 –startvm NAMEOFMACHINE &
Then it should run ok. I run this setting on a Debian 6.x Squeeze since some years. So it does not need VT-x or AMD-V hardware virtualization support, as Oracle says.
“–norwar0” means ”disable raw ring 3″. I still dont really understand this completely. But Wikipedia also talks about the rings.