Hiring fans like that would likely have a negligible impact. After all, which fans do you bring on? There are many fans who enjoy 343’s contributions to to lore. Are they disqualified?
As for the classic conflict between humanity and the Covenant, that would only be able to go so far.If they hired fans to lore check, if they brought on talented writers who understood Halo (Chris Schlerf was the closest, but it only really worked with the Cortana part of Halo 4's story), I think they could turn it around. But they won't.
Clearly I'm telegraphing that they should hire me, because I'd love to do it. Especially if I could fix Halo from what I perceive it has become.
But I do know that, when 343i was just setting up shop, they hired a few members of the fan community. There was that one story-centric blog site, Ascendant Justice, that had to close down right before ODST came out because the guys running it got hired on and chose (or were told) to shut it down despite the popularity and reknown it had for being a highly detailed look at Halo's story. I was actually really sad about that because I enjoyed reading the articles.
There was also BS Angel, couple of others that they grabbed from the community. Don't know what happened to all of them but I know that, however briefly, they were employed because of their impact in the fan community and their knowledge of Halo.
So it happens. Clearly if they did hire people they'd have to be adults with professional work attitudes, but also have a clear and strong passion for the franchise, as well as a deep understanding of what Halo is, is not, and of course, encyclopedic knowledge of the franchise's lore. I see it as no different from the guys they hire for, say, Star Wars and Star Trek movies that make sure things are operating within continuity or figuring out ways to make it work, etc.
EDIT: Lol, other responses while typing this post.