Moved the answer from the "Question" section to the "Answers" section:

Upon further investigation and a test deployment, it seems to work like so:

1. Create the Azure app (creates App project)
2. Create the Web service role named App.Services (creates App.Services project)
3. Create a Silverlight application, have it host in the existing App.Services
4. Create the domain layer project (App.Domain) and add the reference to App.Services
5. (In my case) create App.Tests project for unit/integration testing

Then publish via right-click menu on App project. I created the package and manually uploaded via the Azure account site. The project is listed as 'Busy' in the Azure project, and is unavailable, but everything seemed to work fine.