You have options for "emulation", bochs and qemu are in ports.. neither are viable for "virtualization".. guest OS's will be still quite slow.
Now, 3D acceleration is in its infancy with OpenBSD.. it's not in 4.3 by default, it probably won't be in 4.4 either.. and what little support is there wont benefit Nvidia graphics cards, the only driver available is the 2D only Xorg "nv" driver.
Sorry to burst your bubble...