Given patio heaters etc put out high volumes of IR I doubt they're dangerous for short exposures - you simply don't stand and stare at the element, but I'm not sure I'd like to be blasted directly in the eyes for long periods by eg cars stood in rush hour traffic on a dark night in winter by a flood light style ir illuminator on the front of the car. If you're wondering why I mentioned IR floodlights above, the visible distance and brightness of the picture will depend on the amount of IR in the scene, so just like headlights with visible light, my understanding is the more IR you shine down the road, the more you see. I know in the shooting world, shooters using IR night sights tend to use very high power IR torches with narrow beams to put enough light down to see at distance. I'm guessing therefore that to see a real improvement over visible light, you're going to need a pretty powerful IR light source and not just a couple of low power milliwatt LED's.
As for the hazards, there may be no real hazard to higher levels of IR, I wouldn't know. However, IR is known to penetrate deeply and cause heating of tissues (hence it's use for muscle warming for pain / athletes), so I would have some concerns about high power IR lights and that light striking / potentially warming my retinas on prolonged exposure such as the stuck in nightime traffic scenario above. Without high power lights, there'd be no concerns but as I said above, I doubt you're going to see much difference in distance visibility.
Just some thinking aloud.
