It's not a great a voice but I give it a yay. Especially when he said in Scratch Magazine about 10 years ago how it happened. He would do reference hooks for people when giving them beats (basically singing it for them so they could know how to sing it themselves) and I forgot who he said really did this, but it was either Jay, Snoop, or Clipse that heard one and were like "fukk it, leave it on there with your voice" and then people started wanting him to do it. At least in rap. I dunno about NERD and all that. I wanna say it was Jay on Give It To Me.
So in hip-hop at least I don't think he really ever planned to be a hook guy. It just happened that way. Same thing with Kanye. Kanye does the hook for Never Change on Blueprint. He was just doing it as a reference for Jay, but Jay kept his voice on there instead. Same with Guess Who's Back, Encore and Lucifer for Jay-Z. You can hear Kanye's vocals on there.
If you watch Fade to Black you can see that the hook for Lucifer was already done by Kanye. Kanye had a whole damn song for it if Jay didn't take it.
Check out 1:45