Is it ok for the trunk bike rack to rest against the glass of a hatchback? I feel like this is one of those obvious questions, but I have been unsuccessful at finding an answer (even in the manual for the rack!).  

I just purchased a bike rack (only holds 2 bikes) for my Subaru hatchback. I have found that I can mount the rack such that it doesn't press against the glass of the back windshield, but mounting it so low requires that I remove the front wheel of my bike (at least to make me comfortable, it probably would be fine).  

Can I instead mount it so that the rack presses against the back windshield?  Is this likely or possible to break the back windshield?  

Note that my back windshield is not cracked, though the car is 10+ years old. 

EDIT: The bike rack, which is a Thule Thruway Pro 2, uses two foam-padded bars as the main contact points between the rack and the car.  I figure that this question is probably valid for any bike rack with padded bars as the contact points, not just Thule bike racks.
Being both a hatchback owner and a trunk rack owner, I can tell you yes...and no.

I've got a Saris Bones 3 rack and the feet have etched the window slightly. While the feet are of a more rubbery plastic, I think it's when there's dirt and grit underneath and moves (even unnoticeable movement) it grinds at the window. It usually cleans up pretty well, but I can tell where the feet marks are.

I would recommend putting a sock or other cloth over the feet (the body ones wouldn't hurt either). Also, make sure the contact point is clean, which means lossening or removing the rack to clean behind it.

Lastly, I've never had an issue with the rack slipping or moving, but most of the weight (even on your type of rack) will be going to the lower feet or bars.