You can see the supported database engines by Nolics from here
. This is what we use for our DAL. You can write your application's DAL with whatever you want - OpenAccess, Entity, Linq to SQL, or direct queries.
We will move to OpenAccess for 4.0, but right now we are not using it.
In short, Sitefinity, as of now, doesn't work with it (built-in modules). If you are willing to do so, you can implement custom providers with OpenAccess (a breeze working with it, really), and store your data in any of the supported database engines
All the best,
the Telerik team