There are no tools for OpenBSD, using FreeBSD emulation doesn't sound very efficient.. there are however open source versions of the tools that could possibly be ported one day.
http://open-vm-tools.sourceforge.net/
Not sure if it's maintained or not, nor how much of an effort it would be to port them.
My personal opinion is to avoid all virtualization, it's not worth the problems.. beige boxes are dirt cheap.