Yes, optical guns rely on the screen retrace method employed by CRT monitors and televisions. They pinpoint your aim by timing how long it takes the sensor to pickup the white light that flashes. The screen quickly fills with white, but it does it line by line, top to bottom and left to right, so the game program has a pretty good method of figuring out your aim, but this method doesn't work on LCD. You need an infrared gun like LCDTopGun for that.
The one thing I do know about USB light guns is that they intercept the video signal and only poll your position ONCE, when you pull the trigger. Some games have machine gun options or abilities (like Operation Wolf, for example) and although the original game continues to track your movement while the trigger is held in, emulated games using the "video intercept" method will not re-poll your aim, they're not smart enough to understand. So some games will not be properly playable.