Top-down tracking affects hand tracking, not the view frustum of the Diagnostic Visualizer.
Regarding image passthrough, the Diagnostic Visualizer can be used to view lens-distorted images but doesn't have any mechanism for rectifying the images and does not do the Oculus warping for viewing on an HMD. With regards to images it's mostly a diagnostic tool.
If you just want a reasonable orientation regardless of that, press ->, -> (right-arrow, right-arrow) to start rotating the view at normal speed, then press <- <- to stop once it has spun about 180 degrees. Note that there is also the 'z' key for a mirror view but I don't think that fits the case for head-mounted.
For the best top-down viewing experiences, try some of the examples in the gallery rather than the Diagnostic Visualizer.