Asking because last time I looked the FBSD stuff wasn't "really there". This would seem to still be the situation: "a true (albeit limited) ABI implementation is provided."
As soon as you see “syscall translation”, those are the magic words and they mean that the support is pretty complete. Sure there might be edge cases but if glibc can make a Linux syscall and get good data back, that’s it.
https://www.freebsd.org/cgi/man.cgi?linux