The TopGun wouldn't care if your screen was behind a brick wall.
Its the sensors that the gun cares about, which are two sticks with Infrared LED's to help the gun understand its position, similar to Wii remotes. If you mount these sticks on the outside of the glass, or the side of the cabinet (depending on how wide it is), you'll have no problem at all.
If you're asking whether to mount the LED sticks behind tinted glass thats another story, although I believe Play-Asia.com sell a more powerfull version of LEDs that could do the job?