Bright tracers can overwhelm night vision devices. I dont think that they have any effect on night vision devices right now.
On a side note:
Using tracers help your teammates spot the enemy, but unfortunately they also help the enemy spot you. As far as i know bright tracers only get used as the last bullets of a magazine so the soldier knows that its about time to reload.
Subdued tracers start burning at full brightness at around 100 meters, making it harder to track them back. I think that this would have a nice impact on the gameplay, since it is way too easy to spot people who are shooting with tracers.
Dim tracers dont burn as bright, making it harder to follow them, but they can still be seen clearly with a night vision device.