The first thing that I noticed is that we used SR435 during development, so I was thinking that SR300 might not be supported. But then, you are saying that the camera itself works when you use it in other sample projects? Which sample project was that? I am not aware of any that use RealSense depth feed (but then again, I might be wrong).
In short, can you please confirm that you can see the depth feed from your RealSense in Layer Layouts in a sample project (or a project built from scratch)?