I can confirm that OpenBSD doesn't always work as a virtual machine.
So I would focus on using OpenBSD as the host and using some other OS
as a client in QEMU.
If you insist and I don't know about the latest version, then vmware is
likely much more reliable than virtualbox but still more problematic
than a true install. There is a blog on the virtual box site by theo
stating he can't believe any OS allows the problems virtualbox
introduces(d).
This post by theo was made because developers had wasted their time
fixing bugs that were caused by virtualbox. If anyone does have
problems under emulation make sure you can reproduce it natively before
reporting.
I have several OpenBSD boxes running with no problems on some ESXi servers
