I now have the 12.2 backup working on Linux. However, the restore fails, so the fact that I can back it up is moot.
The error is in the Veeam OrapwdVerifier:
Veeam.Oracle.Linux.Client.System.OrapwdVerifier.Verify(ILinuxShell shell, IShellCommand command)
My SYS password is complex and contains at least 8 characters, but the restore complains of the following:
OPW-00029: Password complexity failed for SYS user : Password must contain at least 8 characters.
Perhaps Veeam internally temporarily uses a non-compliant SYS password before it restores the password file from the backup.
I did not have this issue with 12.1, only 12.2