Duergardo not suffer quite the reputation that thedrow do, nor is their evil one of demon worship and supernatural evilness. With a good backstory, they are permissible as a player character race.
Racial Traits
Duergar bear very little resemblance to their 4e counterparts. The best way to replicate a duergar in 4e is to use the GoldDwarf alternative racial traits for dwarf.