Though it has never been confirmed, I think it is very likely that the messenger in Soulstorm is Ed from the ARG leading up to its release. All the evidence is pretty circumstantial, but I don't see any reasons it wouldn't be.
Firstly, we know Ed was deeply involved with the resistance, as the messenger would have to be to get the honor of delivering such an important item. We also know he was stationed deep in Necrum Mines, which would not only line up with the messenger, but place him in close vicinity to the Keeper.
Ed's disappearance towards the end of the ARG could've symbolized his escape from Necrum Mines as he made his way to the Sanctum where Abe was hiding.
Really though, all of this could be a coincidence. I think the biggest lean in the favor of this theory is Ed's existence altogether. As he never appeared in Soulstorm after so much attention during the ARG, never even a reference, it would make sense that this was why he was so important.
That Ed was the messenger who finally managed to escape only to tragically die in Abe's arms. If only there could've been another way...