I think that wouldn't help any -- nvidia_drv.o needs the kernel module
to communicate with the card.
A Linux X server running under FreeBSD Linuxulater would of course
have no trouble talking to a Linux kernel module - or?
I rather think that the Linux emulation is possibly not
complete enough. (for example I have no clue how to introduce
the /dev/nvida driver here)
Have you tried to use the OS independend XF86 module? If I remember
correctly, the kernel module from NVidia is only to speed up DMA
operations in 3D mode, so the XF86 module should at least be usable. I
didn't know how much of speed you lose, but at least you should be able
to see something. Can you give it a try and report here?