Yes, this is supported.
An advantage of Alfresco is that it can be used as both your back-end content authoring server and your run-time content delivery service. In your front-end site, then, you can have custom forms that can capture content and write out as XML. Once created, you can use our templating service to apply a template (Freemarker or XSLT, however we recommend Freemarker as a simpler alternative to XSLT), generate one or more output files, and than submit to staging. Because this content is captured and stored on the run-time site, the content would then be available on the site, as your run-time server would be configured to serve the latest staging snapshot.
Now the key here would be to have two separate web projects in your run-time: one that is a target for your content authoring server, serving deployed snapshots of your publised and approved editorial content and application code, and a second that is not a deployment target, but rather a target for your front-facing PHP forms that are captured, storing, and serving content directly from an end-user. This separation of the two data source is important, because the first web project is a replica of your published material, meaning you wouldn't want your user-generated content overridden when our deployment engine seeks to sync the remote web projects with the latest changes from your editorial team.
Programmatically, you can leverage your run-time Alfresco instance to do anything you can do normally on an Alfresco box. So yes, creating a new content object, be it structured as XML or be any other asset type, and submitting to staging for immediate delivery is not only possible, but an excellent use of the product.
We'd love to help you with evaluating your migration options. Please let us know how we can assist.
Kevin
