What is the "Chaos" Isolation level and when should it be used?
You can't use it against SQL Server.

It was in DTS: 


Chaos Isolation Level In SQL Server - SQL Server Code,Tips and Tricks, Performance Tuning


And is in SSIS:


DtsContainer.IsolationLevel Property - MSDN


More references, originally added by Nick Chammas in a comment:


Rollback is not supported
SQL Server and Oracle don't support the chaos isolation level