It doesn't work! I've tested it since linux_base-fc6 was commited in the ports tree.
About a month ago, after some discussions in the freebsd-bugs ml and a thread in the nv forum, a temporary solution was found.
The solution is to download the linux driver. The version has to be the same of the installed FreeBSD driver. For example, I have nvidia-driver-180.60 installed from ports, so I had to download NVIDIA-Linux-x86-180.60-pkg0.run
Then the linux driver should be unpacked somewhere.
Once done, /compat/linux/usr/lib/libnvidia-tls.so.180.60 should be replaced with NVIDIA-Linux-x86-180.60-pkg0/usr/lib/tls/libnvidia-tls.so.180.60 from the dir where the linux driver has been unpacked.
Nvidia said that they will ship a driver that install the correct version of the library. In the meanwhile, this is the solution.
I've tested it on CURRENT, where I had linux_base-f9 and now linux_base-f10.
Again, this is not an et problem, it's an Nvidia one. You can see the same using rtcw or other linux-games.