You can load keys into yubikeys if you like (and thus load the same key into multiple devices), but I choose to generate unique keys on-device, so each one has its own (which would make the answer to your question “yes”).
One upside though is that all your keys can go as individual lines in authorized_keys, so there is still only one file to install on remote machines.
One upside though is that all your keys can go as individual lines in authorized_keys, so there is still only one file to install on remote machines.