The Rangers signed 3 minor league players to minor league contracts:
Dusty Brown doesn't have enough major league statistics to be meaningful, so we will look at his AAA stats instead. All of his AAA time was spent in Pawtucket, an International League team, where he put up a .346 OBP, .92 PPG, and 2.78 PAPP, adding up to a 1.37 Simple WAR. According to our AAA metric, his expected offensive output in the Majors should be .300 OBP, .52 PPG, 3.35 PAPP and an O-WAR of -1.58. So obviously Brown isn't even a serviceable major leaguer.
Luis Hernandez has more major league experience than Brown (290 PA). There he had a .286 OBP, 56 OPS +, and .5 WAR (.8 D-WAR). He is slightly below average at second base, but is very solid at SS. His Offense has been poor though, with a .264 win percentage, 2.8 Runs Created per Game, and .121 Secondary Average. There seems to be nothing redeemable about his Major League Statistics, but what about his minor league numbers? He has spent parts of 6 seasons in AAA, mostly in the International League. His offensive numbers looked like this: .284 OBP, .604 OPS, 3.53 PAPP, and .81 PPG. So these are clearly below replacement offensive numbers. The only hope for Hernandez is that his defense will be good enough (as it has so far in his major league career, but D-WAR is terribly unpredictable) to make him a replacement or above replacement player.
Lastly, Yangervis Solarte has not played in the big leagues or even AAA. So we have no metric for Solarte, but it is still somewhat helpful to look at his numbers. Defensively, he plays just about every position (except 1st and Catcher), but isn't very impressive at any of them. In his 6 seasons in the minors, he has a .340 OBP, 1.752 O4S, and walks just 6.3% of the time. Nothing stands out here. I don't see any of these 3, besides maybe Hernandez's defense, helping the Rangers at all.