Skipper imports, exports and visualizes the ORM definitions, this means that Skipper deals with model elements and their ORM properties. @Assert and Symfony classes are not in the ORM scope and Skipper does not import them.
If you use XML or YML format, these are not part of the definitions.
If you use annotations where @Assert and all Symfony classes and properties are kept together, Skipper will properly separate them. This means that only @ORM annotations will be imported, and only @ORM will be changed upon export, but you will need to add and modify @Assert and other Symfony properties manually.
We may add support for another classes and annotations in the future, but it is not on our short term plan.