Only if you enable iCloud Keychain, which is locally encrypted and synced in encrypted form. https://support.apple.com/en-us/HT202303 has links to the details.
It's not useful though as you shouldn't share ssh keys between machines anyway.
It's not useful though as you shouldn't share ssh keys between machines anyway.
Are you talking about public or private keys ? I see nothing wrong in using same public key to log in from a particular machine to a number of remote machines.
There is nothing really wrong with it; it's a good way to reduce the burden of managing secrets. The downside though is when multiple remote machines need to be contacted because a private key was revoked. Then again, a common need for revocation is a compromise of the machine on which the private key(s) is stored, which can often mean a number of private keys need to be revoked. I think the ideal is still to have unique key pairs for each client-server combination.
The most likely cases are that (1) the client machine was compromised, or (2) an un-encrypted backup was lost. In either case, I have a hard time seeing how one private key needs to be revoked but others on the same client machine don't.