GP's link is to the COMPAT_FREEBSD binary compatibility for earlier versions of FreeBSD, oddly. I don't think it (or linux emulation) has anything to do with Nvidia's needs re: CUDA/NVENC.
It means you have a module from some vendor, or something similar to the NVIDIA installer for linux, which technically is nothing else than a batch compiled makefile, spitting out a kernel-module made for version 1.2.3 while you are running 2.4.5. It worked. I don't know why it shouldn't now.
Edit: I'm not having any FreeBSD systems in use right now, so i don't know if they changed the defaults. What i remember is at least the last two versions were compiled into GENERIC, so you didn't even had to compile your own kernel when that range backwards was enough.
Similar thing in NetBSD, a loooong time ago, even their own driver for 3Com905 relied on the equivalent of that functionality. That caught me by surprise, because i used NetBSD like Gentoo, found some Compat foobarjurassicBSD, wondered why i should use that at all, and had no working net. Fun! :-)
That's not how the nvidia binary blob works in FreeBSD. Instead, there is some compiled-from-source-code OS portability glue, which is compiled against the target version of the FreeBSD kernel. Then the binary blob links the portability glue.
I believe something similar is done in Linux. The difference in experience may come from FreeBSD maintaining a stable KBI over a release version (e.g., stable/12), while Linux aggressively does not maintain any KBI stability; hence the need for DKMS/akmods.
Sigh. Been typing too fast as usual. I know thats not the way the Nvidia-thing works, instead doing the glue-thing which interfaces to the binary blob like you mentioned. But it could (instead of that)! That's what i meant to say.
