Your night vision project actually sounds really cool! I like the idea a lot. Talk about bring the future into the palm of your hands.
I think your logic on the LEDs and voltage checks out. Usually anything under driven is safe. The reason for resistors with LEDs is sort of a safety thing, so I think it cancels out in this case. Remember that over driven LEDs sometimes... just blow, rather than stop working nicely.
I think the regulator you selected would work, but you'd probably need two. One to drive the LEDs and one to drive the Pi. I'm not entirely certain about driving the Pi with it though. There's a tendency for cheap electronics to introduce jitter. That is to say, slight fluctuations in the power that might cause unexpected consequences in the Pi. I definitely would not connect it to the GPIO header as that by-passes all the currency protection in the Pi, particularly the self-resetting fuse.
What might be a really good fit for you might be the MoPiMoPi board. It's a little bit more expensive, but takes care of all the regulation and good stuff when using battery power. For example, it'll inform the Pi when the voltage gets low and trigger a nice shut-down. Or you could do it with the battery button. It also runs the Pi for around 10 hours on 8 rechargeable AAs. There's probably plenty to spare there for powering your LEDs and the rest of the equipment for a decent bit. Or use a large sealed lead-acid battery.