As I mentioned in my post on starting pitching depth, pitching depth in general for the Yankees is pretty weak. It's even weaker for relief pitching prospects mostly because pitchers that could be decent relief pitchers in the major leagues are most likely starting pitching prospects--relievers like Dellin Betances, Adam Warren, and even Mariano Rivera, all began as starting pitching prospects. Very few prospects come up through the system as relief prospects because that already marks them as a flawed product to begin with. Nonetheless, the Yankees have a few relief prospects of note, some that may even contribute to the big league club in the near future.
Unlike with starting pitching depth, the RailRiders have the most readily available relief talent that is close to major league ready. There is Mark Montgomery, a prospect who, at one point, was considered to have closing potential. So far this season he's pitched to a 2.49 ERA in 21 innings with 29 strikeouts. If he continues, he may be a late-season call up, but I wouldn't expect him earlier. He's still only 24 years old and I doubt the organization would want to start the service time clock any earlier than they have to.
There was recent call up Jose Ramirez, who was brought up as the 26th man for the doubleheader against the Cubs. He's only thrown 5.2 innings so far this season but has also only allowed one earned run and has struck out eight. He could be an option to fill out the bullpen if injury strikes. Then, the Yankees have options in both Danny Burawa and Robert Coello, two pitchers that we got a look at in Spring Training. Coello was absolutely dreadful in the spring but has since allowed only one (!) run in 17.2 innings while striking out 24. Burawa too has impressed in Scranton and has not allowed an earned run in 12.2 innings while striking out 17. There's a clear pool of relievers who could contribute to the big league club in a short time frame.
The hopefuls (in regards to major league talent) get much less hopeful as we head to Trenton. The Thunder rely heavily on a handful of relievers, most of them being older minor leaguers who probably won't see major league playing time. There is Manny Barreda who has pitched well--an ERA of 2.00 in 27 innings –but, he's already 25 with more development to go. There's also Fred Lewis; he's already 27 and has struggled in both Double-A and Triple-A this season. The two youngsters in the group are Cesar Cabral (of three hit-by-pitches fame) and Tyler Webb. Both of them have posted ERA's over 4.00 in limited time, so neither are banging down the door.
While Trenton has its share of older journeymen, Tampa is stocked with youngsters who could be sleepers if they continue to impress in this level and beyond. They have pitchers--Dietrich Enns, Nick Rumbelow, Alex Smith, and Phil Wetherell--who have all pitched to ERA's under 2.00 and are quite young as well. Whether they perform when or if they move up a level is yet to be seen, but they'll certainly be interesting as far as depth goes. Kyle Haynes and James Pazos round out their bullpen and have posted ERA's slightly over 3.00 in about 22 innings each, so they'll also be interesting options going forward.
I mentioned previously that the Charleston RiverDogs have an especially strong rotation. It has been extremely competent so far, but they work in the same way as the High-A crew: they're performing well, but who knows how they'll fare when they move up a level or two. They've gotten excellent relief appearances from Rony Bautista, Jaron Long, Chris Smith, and Cesar Vargos who have all posted ERA's that are 2.63 or lower in their limited appearances. Jordan Cote and Angel Rincon have been shaky, but as I mentioned before--the samples are limited. All of these pitchers have performed well, but we'll see what happens when they move up a level and expose their weaknesses to better competition. There are no clear "prospects", but it'll become more apparent as they all develop.
In developing relief pitching depth, the strategy should be the same for finding starting pitching depth. If one drafts the best talent available, a flawed starter can always slide to relief and be effective as well, like Betances and Warren have done. Often times one does not see that until later in the development process (which is why the roles are more defined in Triple-A), but having the talent there to make the transition to begin with is the biggest challenge. I don't think a good season could make this system elite in its possession of relief prospects, but good drafting in the lower rounds and some good performances will certainly help its outlook.