> I am wondering if it is possible to rig up Docker to work in that?
Unlikely, 99.9% the answer is no (at least not currently).
FreeBSD does not have “full kernel emulation”. What it has is a table mapping linux syscalls to freebsd equivalent, essentially an adaptor. This, along with a typical linux runtime (glibc and other libraries) means that you can execute linux binaries.
But this goes as far as the translation table goes.
To run docker containers you’d need an equivalent syscall to create (pid, network, uts etc) namespaces and (cpu,memory) cgroups.
There is no equivalent of those syscalls in FreeBSD at the time of writing, as far as I know.