How does the DAS cope with IMC conditions?
I don't know, but I would venture a guess that IMC performance is similar to most other IRST since the physics are the same. That assumes NG has not come up with a clever way around the inherent limitations of the IR spectrum.
That being said the 900 to 1700 micron wavelength sees thru haze, mist and fog very well. I am not certain, but I understand that DAS's sensor spectrum includes this range.