Underdark ranger, Hide in plain sight (outdoors)

[Simian]

Unfortunately, ever since day one, the game has not been able to distinguish a day from the night. Thus, if the Underdark areas are set to outdoors, you will see the -1 penalty regardless of lighting or time of day.

Drow and Grey Oc have Light Blindness, Deep Gnomes do not.

Duergar have Light Sensitivity, which imposes -2 penalties.

Anyhow, in addition, according to NWN2wikia, Light Blindness does not impose real penalties, it only adjusts the character cheet.
"The attack and saving throw penalty are only applied on the character sheet. They are not applied to the rolls in game."
http://nwn2.wikia.com/wiki/Light_Blindness

It should be tested out.

However, if the information listed on the NWN2wikia is correct and as a direct result you decide to set UD areas into outdoors, according to the wikia the Duergar penalties are still very much real. (They would be forced to select the Daylight Adaptation feat on level one.)

[Eldebryn]

Yes although you could conceivably set all such areas to night at all times. I think Drow don't get -1 at night correct?

I would guess so, though I have seen more than enough bugs in this game to be convinced that they may actually get a -1 at night... would need to be tested.