Looking directly at IR lamps is never a good idea since your eyes do not react to the bright light so don't protect themselves by closing the iris. The high power security IR lamps can be a real hazard if you get too close, normally they are put well out of reach. There are no other health issues, the IR light is only just not visible, no real difference in effect to red light, it is not the same as the IR from an infrared heater.
I've not seen any regulations that seem appropriate, so I suspect there is no regulation for dashcams, even though I think there should be for what is an invisible hazard, in the same way that lasers are regulated. I think the current intensity is regulated by the availability of cheap IR emitters, the cheap ones are safe, and the unsafe ones are too expensive for dashcams.
The amount of IR needed by dashcam using current image sensors to see reasonably well is not an amount to worry about unless it comes from a single IR emitter, if you come across a camera that produces a very sharp interior image in complete darkness then it might be worth asking questions. Note that on the Viofo A139 they are using 6 IR emitters rather than the normal 4, so can get improved quality from increased brightness without using brighter individual emitters.
Still, never stare at any IR light source, it is probably safe, but you can't see if it is safe. Most visible LED torches come with a warning not to look directly at the lamp, IR dashcams probably should too.
