Diaz, 27, was drafted by the Toronto Blue Jays in the 12th round of the 2006 draft. He's had a rather undistinguished minor league career, reaching base with some regularity but doing shockingly little when it comes to actually hitting strikes. Believe it or not, he comes in with a career slugging percentage of .294 in 2712 plate appearances. Defensively, he was ranked the best infielder in the system after 2006 by Baseball America.
Mark Hamilton, 28, was a second round pick by the Cardinals in that same draft, and actually made it to the major leagues for a couple cups of coffee in 2010 and 2011. Down below, he had been excellent at the plate in his last three seasons at Triple-A Memphis before a down year in 2012, perhaps caused in part by a quad injury that cost him the start of his season.
Neither of these signings are particularly interesting, of course. Hamilton does have something of a Jeff Bailey feeling to him, and might see time with the Red Sox in case of serious injuries, but that's a long shot. Perhaps more likely to see some time would be Diaz if the Sox were ever in a situation where they needed a backup shortstop but didn't want to take Jose Iglesias away from everyday at bats. Diaz has been seeing less time at the position of late in favor of second base, but he's still able to play the part.