Olt was a strong candidate for an AFL slot before he got hurt, and makes even more sense now, after having missed two months of the season. This gets him the opportunity to get some more at bats.
Neil Ramirez is at just 92.1 innings so far this year, after missing some time to allow his arm to rest, so this is a way for him to pick up some more innings.
Miguel de los Santos, like Ramirez, has missed some time and not logged a bunch of innings. I think the Rangers also would like to get a better look at how he does against higher level competition, after he struggled in AA and spent most of the season in A ball.
Johan Yan is a converted third baseman who is now pitching, and who has a 1.12 ERA in 60+ innings in A ball this year. As a Rule 5 eligible guy, he's someone the Rangers probably want to get a closer look at versus higher level competition.
The rest of the squad is primarily fringey prospect types, although they could end up on the map with a strong AFL.