It seems the RadDataGrid for universal apps does not want to be provided with data ;-) All the necessary hooks are declared internal.
The only thing I came up with is attaching to the sort and filter descriptors to a SimpleODataSource. But this is quite ugly, because the grid additionally still tries to filter on its own. Additionally, when using the "StartsWith", etc. filters, OData returns case-insensitive filter results and the grid applies case-sensitive filters afterwards.
I've attached the relevant files of my experiment to make the grid operate on a Microsoft.OData.Client.DataServiceContext (note that I added the ".jpg" extension to the zip as it is one of your "allowed extensions").
1) How to make the grid use case-insensitive filters?
2) How to convince the grid to just use what it has been given via the ItemsSource and not to sort and filter on its own?