While you can't immediately prompt with a dialog, like the rename warning, you can still write a workflow. Generally, the way I do stuff like this is to have workflow that monitors the intake folder in order to act on incoming documents. The first activity will be Invoke Workflow for another workflow that looks for violations of various validation rules. It sends an email to the person who scanned/imported the document and renames the document to something like this: "*Missing or invalid field: Client Name*" and returns a Boolean. If it indicates a failure, the calling workflow completes without taking any actions and leaves the document sitting in Intake until someone fixes it.