As it stands right now, one of the biggest questions for the Rangers is centerfield. Julio Borbon probably deserves to be given a shot because a solid prospect shouldn't lose all of his sheen after one poor season, but he certainly does not inspire much confidence at the plate right now. The alternative is starting Josh Hamilton in center and David Murphy in left, but you would have to be concerned about Hamilton's health if he's playing centerfield every day. Some depth in the outfield, particularly someone who can play center, would be nice. Now, Hairston is primarily a corner outfielder, but the Padres trusted him in center 19 times last season, and, for whatever it's worth, UZR has him as having saved 5.4 runs above average in his 125 career games in center; DRS has him at seven. That's a small sample size to go with the questions that come from defensive metrics, but there's some evidence here Hairston is just fine in center if you need someone to fill in.
More importantly, though, the Rangers could use a right handed bat. Whether you have Murphy or Borbon on the bench regularly, you've got a left handed hitter. You have one more left hander if, as the link suggests, you have Chris Davis as the 25th man. Hairston just happens to swing bats while standing in the box to the left of home plate in the fashion of a right handed hitter. Further, while his career .320 weighted On Base Average is none too inspiring, his career .355 wOBA against left handed pitchers sure is. It dipped a bit last season down to .291, but so far in his career, that's a blip on the radar, and some of it was playing in Petco Park. Or a lot of it, really. Oh, and some of it was his .236 Batting Average on Balls In Play, as opposed to a .278 career, despite only a very small downtick in line drive rate. So there's that luck dragon stuff, too.
Looking at a quick projection, using ZiPS and a wOBA calculator, Hairston projects to hit about .320 (neutral park) with a slash line of .240/.306/.395. Again, that slash line isn't too inspiring, but we want Hairston for his ability to back up all three outfield positions and hit lefties, and we also don't intend to play games in Petco. At his career split ratio, that projects to be a .350 wOBA against righties. Closer to .360 for someone who hits at Rangers Ballpark in Arlington. For reference, that would put him ahead of every regular on the 2010 Rangers but Ian Kinsler (.425), Nelson Cruz (.412), Vladimir Guerrero (.401), and Michael Young (.378) against lefties.
So, for the too long; didn't read: Scott Hairston can probably fill centerfield in a pinch, and can be expected to hit lefties better than most of the team. That's useful.
He's a player that didn't even occur to me until recent Lone Star Ball discussions, but he's a nice fit, and now I think I really want him. The key, as Adam says, is how much he wants and whether or not he wants to start. It would almost certainly be worth the Rangers' time to find out and see if they can make it happen.