Alright, so going by the complete lack of any response I assumed that no such schema exists. So I set about creating my own. With the exception of fixing typos and not requiring skipFrom and skipTo properties in the CSV Transformer, this schema should match up with the OrientDB-ETL Configuration documentation
as of 2015-07-23 20:56 UTC.
That said, it needs testing. All the working ETL config files I validated with it checked out, but I'd appreciate if others would give it a shot and tell me if it validated their config files successfully for them.
I also tested Visual Studio autocomplete and it seems to be working as well (see screenshot below).
Please let me know if you find any issues.
EDIT 2015-07-27 14:03 UTC - Updated the JSON file to remove quotes around a boolean default value in the Extractor section.