Alex (who is not related to actual prospect Nick) Castellanos is exactly the type of guy the Cubs should be trying to get to fill the bottom of the 40-man. Like Mat Gamel, he is a former prospect (well, sort of, in Alex's case) who just never put it together at the majors. However, Mat and Alex struggled for completely different reasons. Alex put up solid numbers in AAA (not mind-boggling, but a line of .257/.347/.468 last year, and a .328/.420/.590 line the year before that), but as a member of the Dodgers organization never really received more than a cup or two at the major league level. Gamel was considered an elite prospect, one who might stick at 3B but was essentially a bat-first 1B. Injuries and ineffectiveness quickly took the luster off, and Gamel now is just fighting to make a roster at this point.
At first blush, Gamel is the more talented player of the two. He has the pedigree of a top prospect, as well as the perceived ability to play at third. However, the former isn't all that relevant, and the latter is wrong. Gamel has had a long, extensive injury history, with everything from a right ACL surgery to a right shoulder train to whatever a big toe sesamoid removal is. The ACL has sidelined him for 2 consecutive seasons. At this point, Gamel is a left-handed bat that can play at 1B and maybe RF, if you squint your eyes just the right way. Alex Castellanos was demonstrably great at AA and AAA in 2011 and 2012, and is a right-handed OF who can play the corners well and center passably. He can even play 2B and 3B in a pinch. Considering the handed-ness of our OF right now (Sweeney, Bogusevic and Schierholtz are both lefties, so are Choo and Ellsbury), Castellanos is exactly what the Cubs need right now.
I'm not saying that Castellanos could ever start for the Cubs (though I'm not sure he's not better than Sweeney), but he makes so much sense as the RH side of the CF/RF platoon, someone who could even play 2B in a pinch. I'd be shocked and frankly disappointed if the Cubs didn't claim Castellanos, should they get the opportunity. Gamel has no future on this team even if he comes back 100% from his injuries (what do you do with a LH 1B when you have Rizzo?), but Castellanos certainly could (albeit short-term).