I do not think that dual wielding assassins are any more overused than any of the other clichés in the fantasy genre. As Lord Xia said, fireballs and dragons. I did ask about Nym sometime ago, but the folks at Stardock never replied to it.. I was hoping he'd make a return to FE or LH. Maybe he will yet!
Now.. Drizzt is a badass, of that there is no doubt. However, I doubt he is the origin of the appearance or frequency of characters that dual wield, most notably assassin/rogue-like characters. I can't rightfully say where the inspiration comes from, but may have something to do with the Areani (a group of spy/assassins dating back to ancient Rome) and other groups like them. But I don't know for certain.
Speaking of dual wielding dudes.. You can't mention it without at least giving some love towards Miyamoto Musashi. Now that guy was a dual wielding badass, among other things.