In one of my main sites, I use SubSonic as the DAL.  As long as you're not building modules to sell or release to the public, there shouldn't be any problems with using it.  You would just need to make sure to properly version and maintain database updates on your (hopefully) separate database and correctly synchronize the updates with the module version(s) that are installed and hitting the database.

Also, you would no longer need the SqlDataProvider files and classes.  And in the App_Code directory, the only file that may be necessary is the controller class.