Flat tables are by far the most common data model for SAS VA. Star schemas can be used but personally I've never found a need to use them so far. The main reason for using a star schema is to reduce storage requirements, with the downside of greater complexity.
However you can also reduce storage requirements for flat tables by combining the use of short character codes and user-defined lookup formats. In effect you are applying the star schema lookup capability without the complexity by using lookup formats.