I figured you were implying that Jarlaxle was actually Drizzt's brother somehow. I doubt that if Jarlaxle was half-drow that there would be any way he would have survived so long in Menzoberranzan -- also, he has all of the innate drow powers fully, which half-drow wouldn't.

Though, they don't really go into Entreri's background nearly enough. I figure it's because in the early books, he was painted as just a bad guy for the sake of Drizzt being a good drow with an evil human counterpart. However, the more his character is delved into, the more interesting he becomes. I dunno. Drizzt used to be a lot more interesting, but what is there to say about him at this point?