Seam and JSF doesn't force any kind of design pattern on you.
JSF in general is built with dependency injection as a cornerstone and Seam uses and enhances this functionality.
So you can define your service anyway you like and inject the into the backing beans( which are called from the web interface), the backing beans would then delegate to your services.
Make them Seam components and use them as you wish. In general, I think you'll find that you can define your entire application in terms of those "service layer" things and write very little in terms of glue code. (the "action" layer, as you describe it) Where you can't, you simply layer your application. There's absolutely nothing tricky about any of this.
As to the DAO issue, I think you'll find in Seam that if you are doing anything tricky you'll want to use some sort of controller object to manage your entities. That's what the EntityHome and EntityQuery objects do in Seam. If you are forced to over-architect your application, you'll probably end up either modifying your DAOs to actually perform some useful functions in the context of Seam or creating a controller of some sort that delegates off to your DAO.