As I know eXpressApp Framework (aka "XAF"), your question cannot be answered with a straight "yes" or "no". XAF has many traits that makes it an awesome platform for a modularized system, but it also comes with some limitations. If you want to use a legacy database, XAF will do a great job in generating persistent classes and a working interface (WinForms and/or ASP.NET) for you. The built-in security-system will let you grant permissions to those classes (and related listviews and detailviews) in a modular way.
However, any logic contained in stored procedures will not be usable automatically and any existing presentation layers will not be easily incorporated in a seamless way.
But since XAF is really customizable, capable, mature and well-supported, I would advice you to give it a shot by downloading and getting to know the evaluation version and contact DevExpress support with the questions you have. Both resources can be found here http://www.devexpress.com/products/net/application_framework/.
Good luck!