How to Retrieve FID from UUID on Feature Enable
I guess i didn't know exactly how the export/import works...perhaps, i still do not, but here is my theory so far. When importing custom fields containing file, we have to save the file in the table file_managed by ourselves. The feature module will only do the work of importing files for the default field types(file, text,etc) and not for custom fields which is our case.

Here is quick write up
http://margotskapacs.com/2014/03/make-custom-field-with-file-exportable-in-drupal-features/