I, too, have a backup camera mounted for the purpose of hitching up and I like it really well. However, I mounted mine on the outside of the back glass so I can't help directly with the question of viewing through glass. I can say that I mounted mine outside because of training I had in my former occupation that led me to believe that shooting through the rear window may result in issues with clarity and reflections that I didn't want to deal with.
One thing I can mention is that I often had an issue differentiating the black pin box from the black hitch in low light situations. My solution was to place a strip of reflective tape on the front of the pin box. I wouldn't recommend this. The reflection from the IR LED's overpowered the lens and nearly washed out the image; I think it was worse that the problem I tried to correct. Hope this helps