Does Nas need an executive producer? No
Would he benefit from having one? Yes
Why? Every album Nas has done up to this point has had someone co-executive producing with Nas. The exceptions are Illmatic (Faith Newman and MC Serch executive produced this one), Nastradamus (Nas executive produced this one by himself), Stillmatic (credited to Destiny, but more than likely this was Nas too for obvious reasons), Hip Hop Is Dead (Nas executive produced this one as well).
All of Nas's best albums have all had someone else executive producing with Nas or took they took the reins completely. Stillmatic is the best album that Nas executive produced by himself and even then some great songs were left on the cutting room floor.
The Benefit of having someone else executive produce- Objective ears and fresh perspectives. Nas is an incredible MC and artist. Still, having someone compile that genius into a cohesive playlist that is consistent throughout could help tremendously. I mean, sometimes Nas's most creative ideas don't always make for good music. In those cases, some songs that were dope were scrapped and the ill concept that isn't pleasing to ears made it. For example, "Who Killed It" is an ill concept with a dope beat, but the whole accent is overkill and ruins the song.