Hi Andre,
In general this is possible, but unfortunately we don't have such an example. One way to implement this is to project the surface points to view coordinates and check them against the selection rectangle.
You can take a look at the following example in our Windows Forms demo application. It shows how to transform points from 3D scale coordinates to 2D viewport coordinates:
All Examples > Coordinate Transformations > Scale to Viewport
Best Regards,
Nevron Support Team