J Lo: I'm not sure if that would work. How would they meet each other? What would the story that connects them be about?
SPOILERS!!!
All right, maybe not a full game. But in BG2 you travel to another plane in a quest, and in PT you travel a lot through dimensions. If they got a Drizzt cameo, why not the Nameless One.
In a way, they are similar. Bhaalspawn is a child of a god, whose mother was killed by their adopted father. Of course, Nameless One has a much more tragic story, because at the end of ToB you can renounce your divinity, while Nameless is stuck with his 'gift' forever. However, they both are extraordinary and both struggle. I mean, Bhaalspawn's story (no matter what ending you choose, i went with embracing divinity) is not a cakewalk, either. He has to kill 6 of his siblings (Sarevok + the Five) and has his soul stolen by Irenicus, even if manages to regain it.