After a year(!) of looking around, it is still a more than desperate situation on FreeBSD utilizing OpenCL (or CUDA). The nVidia driver are good, but incapable of providing OpenCL or CUDA to FreeBSD. Why is that so? The frustration can not be larger.
I tried also to find platforms where nVidia is present looking for "votes" for supporting FreeBSD and maybe other *BSD UNIX systems, but there wasn't any evidence nVidia has ever made statistical requests that reflects the recent situation and the wish of customers.
If there are platforms where this can be discussed others than this, please let me know.