Can we invite external reviewers,e.g customers, without giving them complete access to the software?

Customers can be added into the software at the no access level; they would not be able to login to see reports but they can complete customer satisfaction evaluations.

Be sure to add the user as a customer contact on the project that needs to be evaluated, so that all the evaluations completed by a customer are categorized as customer satisfaction scores visible on the person evaluation reports.