An “error pipeline” might not be right for you if you want specific processing for various types of errors that various snaps can give. In my opinion this would be for more generic error handling, and there are usually pretty standard fields ($error, $reason, $error_entity) that you can throw to logs or whatever for troubleshooting.
For specific error handling on different snaps within your pipeline, you might want to put the error processing on the snap’s error path itself. For example, “pull the pug” (can’t connect) type errors, you should be able to test your sad/error paths by trying to hit something else (bad url, etc.) rather than asking your vendor to kill their site… I’m sure you can figure out how to test your code without the participation of your partners.