StrataFrame security is supported on WebForms and you can use the ASP.NET roles and SF separately.  They are not integrated with one another as the SF engine provides more overall functionality.  You can use them in conjunction  though it the need arises.

As for a 3rd party tool, I would look towards Infragistics since they provide AJAX controls and have a nice new feature with the Application Styling.  Ultimately you can use any 3rd party control you like.  But for a preference, I would more than likely look towards Infragistics.

If you have an internal graphics person, the 3rd party controls really do not buy you that much since most data entry is not much more than dates, check boxes, radio groups, and text boxes.  The only reason to go with a 3rd party for web is if you are wanting to have dynamic skin features or more sophisticated controls like chart controls, etc.