There are five living Hugo Award-winning writers in Star Trek: Harlan Ellison (The City on the Edge of Forever - 1968), Morgan Gendel, Peter Allan Fields (The Inner Light - 1993), Ronald D. Moore, and Brannon Braga (All Good Things... - 1995).
No one has ever won a Nebula Award for Star Trek.
But he did not suggest Nebula and Hugo award winners for Star Trek. He just said "I'd like them to give one episode to each of the Hugo / Nebula award winning writers alive." That would certainly change things if he meant only Star Trek writers, sure.