Linux yes
Linux yes. Live CD no.
This setup may be immune to tampering but CD reads could still fail.
A better setup would be a custom Linux distro that’s not even a full OS but rather a custom program that only knows how to receive votes and send results. Something akin to the interface on the Nordson Logicomm. It’s basically the Linux kernal with a program for monitoring and controlling industrial gluers on an assembly line. Even with the units connected to a network, they are only capable of sending production data and receive nothing.