I've corrupted PCs before. It happened when I was running Gary Gygax's Necropolis, and then later in my homebrew Greyhawk campaign (the latter PC is now a recurring NPC antagonist).
Is Nightbringer going to try and corrupt Greg's Dragonborn Cleric? Absolutely it is. (I also have a nice set of notes from which to start, thanks to the designers at Wizards: artefacts in 4E are presented in the best way yet).
Nightbringer has its origins very much in Stormbringer, a sword that I'm familiar with, but I don't think Greg and my other players are - they're too young. (Scary - I'm now closer to 40 than 30). The works of Michael Moorcock were one my early loves, and a couple of campaigns I played in - especially one memorable Amber game in the 90s - were heavily influenced by his works. Now, I don't think my players have read any of his works!
Badwe: Yeah, that sounds fun. The orb in H3 was one of the highlights of the module for us.
(If any of you have P3, go and look up what Wizards' have written about Nightbringer... and there's more in E2)
Cheers!