I think you'll be pretty much flying in the dark. I'm sure the duergar exist beneath the lands you talk about, but the area is better known for its humanoid hordes than gray dwarves, drow, or other underdark races.
In both the old slavers series and the old Pomarj accessories there were a few duergar NPCs, and I think the Abbor-Alz has an active population of duergar. Drow have been seen in the Suss Forest, attacking the settlements in Celene, but no duergar.
I'm pretty sure Duergar are a racial choice in the Psionics Handbook (though I don't own it). Presumably there's info there, plus you'd have the benefit of throwing psionics at them -- a challenge most would find new and unexpected.
I'm always for taking players out of their comfort zone :)
Later,
Jack
Hey- I have written a Huge adventure all about Durgear!!!
They are my favorite... here is a little quote from it...
The Durgear move by night and entomb themselves by day in underground caverns. During their nice stay with the Durgear ( who call themselves, translated to common “The Grayish Orderlites of the Impassive Infantry”) the party will come to see the Gray Dwarven nature like none before. The utter regimentation of the troops, the incredible loyalty to a superior at all times is astounding.
This loyalty is tested in a rather trying way. On occasion a disobedient Durgear is forced by his jeering Commander and comrades to don a suit of plate armour. One greatly feared as “Ye Smelly Encasement”, as a means of a horrible punishment the poor creature is forced to wear it for days and days. Through observing the bathroom habits of the Durgear, the players have learned that they have a rather unfortunate condition of “Bowellus Uncontrollus”. Having a diet composed of 70% fungi and badly brewed alcohol probably does not help this.
(At the witness of this punishment the party may become suspicious of Grunnipalg as they have never seen him out of his Ornate Field Plate.)
The low hum of the continual under the breath grumbling. The Grey Dwarves are consumed with bitterness, feeling that their race has been forever denied what was rightfully theirs. The pure bitterness of the Durgear manifests itself as an actual smell as they see life as nothing more than a backbreaking torment from birth through to death.
They have little mercy for the weak or helpless and enjoy tormenting each other in a very mean way. From a young age they are quickly schooled in the harshness of the world, taught that their lot in life is nothing more than a never ending grind accompanied by betrayal and then death. The party will see the strange foods that the Durgear eat and have a taste of it as each day a few wizened sticks of something black and some grey goo is put into their cage for them to eat. The sticks taste like bitter blood and the goo tastes like dirty bitter radishes. The party will pick up basic Durgean terms such as “kill it”, “crush it”, “I dare you to eat it” and “ Ye Smelly Encasement”. They will experience the full hatred Durgear have for all things as they refrain from harming the players with a pained self control.
The Gray Dwarves have little understanding of the above world and find the concept of vegetation and some of the creatures they encounter not only amazing, but sadly inedible...
Five days will grind by with the players laying about in the cold wobbly cage.
In fact they could be described as horrid little bastard days as with an evil deliberacy they drag on....
...and on...
...and bitterly on...
The party will find “dark” and “grim” and “bitter” to be the best words to describe the Durgear as a species.
Module is at http://www.rpgarchive.com/index.php?page=adv1&advid=808
Email me for the maps