Well "Arista kit" is rather broad the DCS-7050QX-32 has AMD onboard but I am not sure FreeBSD would work on it. https://forums.servethehome.com/index.php?threads/arista-dcs-7050qx-32.11132/
I wonder what the ethernet driver it would use for one. These are specialized high speed routers compared to say Sophos firewalls which really do use commodity hardware and are reachable via serial console. Firmware/BIOS would be the next question. Is it accessible or locked down.
I don't see anybody using anything other than EOS on them.