With regards to the failure not being logged or visible enough during migration this is a known issue for us and we busy working on it.
Which mode does the Migrator use? Does it use batch?
It uses batch mode but batch mode does not disable validation. At this stage there is no way to disable validation because if a validation error were ignored or missed the underlaying object model would become partially corrupted and there is no simple way to recover from this. In the future we may add an option to disable validation but its not something we looking to do for the moment.
Maybe if you share the errors you are seeing we may be able to help you work around your current problems.