And one more question regarding styling: Is it possible to embed the Scout Web App into a HTML page (I want real embedding, not just using an IFRAME)? Is there somewhere a template that can be customized?
Yes it is possible to style your application. The Scout Rayo L&F is separated in the bundle org.eclipse.scout.rt.ui.rap.theme.rayo. So all you need to do is make your own theme bundle and change the scout.css included in the rayo theme to your need.
You have to consider that the css is not consumed by the browser but by the RAP Framework in the UI-Server. So not everything is possible which can be done in css3 .
You can find an introduction in RAP Theming here:
For your second question about embedding I have to ask for your patience. I'll write an answer the next 24h.