Hard to say. Certainly his name would have been a draw, but you've also got Altman, head of YC as a founder, not to mention his buddy Peter Thiel.

Musk's influence in attracting/retaining talent is rather a mixed bag given that he poached Karpathy for Tesla around the same time he left.

I think the person you're thinking of who Musk helped recruit for OpenAI is Ilya Sutskever. The person who just left, after a second brief stint at OpenAI, is Karpathy who for time being seems content on going back to his roots as an educator.