The Dallas Cowboys are a very good football team and have a deep roster to prove it. From top to bottom they have arguably the best depth they have had in several years, which will make it really difficult to earn a spot on the Cowboys roster. This is especially true for the rookie draft class, but might be nearly impossible for any undrafted free agents.
The Dallas Cowboys have been known to find some hidden gems from the undrafted free agents they have signed in the past. Ronald Leary, La'el Collins, Cole Beasley, Barry Church, and Jeff Heath are just a few who have come in and not only contributed, but become starters. But, this year UFAs are going to have a really hard time earning a roster spot.
The Cowboys can only carry 53 players on the roster heading into the 2017 season, and a lot of those spots are already spoken for. All of the other Cowboys roster spots are few and far between, which makes training camp extremely important for these undrafted free agents.
After scouring over the Cowboys' roster, there aren't very many names that stand out among the UFAs. In fact, I think there are only three that have a legitimate chance at earning one of those coveted roster spots: RB Jahad Thomas, OL Dan Skipper, and OG Nate Theaker.

Jahad Thomas, Dan Skipper, and Nate Theaker should also be considered longshots to make the Cowboys roster, but I think all of them have a slight chance if they can prove themselves worthy. But, each one of them is really going to have to catch the coaching staff's eye in training camp and prove themselves better than their competition.
Of the three, I think Jahad Thomas probably has the best chance to make the Cowboys roster. The offense could you really use another receiving type back after the departure of Lance Dunbar in free agency. That is probably Thomas' best trait, but he's really going to have to improve in all other areas of his game. It's going to be difficult, but he could take over that Lance Dunbar role in 2017.
Dan Skipper is a big man (6'10”, 311), and is hopping to throw his name in the hat for one of those vacant offensive line spots at either offensive guard or tackle. The Cowboys have been working him out at guard, but he was a fixture at OT during his tenure at Arkansas. His biggest hurdle that he needs to overcome his blocking technique. If he can improve that, he has a chance to make the Cowboys roster.
Of all of the undrafted free agents, my dark horse to make the Cowboys roster in 2017 is Nate Theaker. He played both tackle positions at Wayne State and also right guard. He has the size teams look for in an offensive lineman (6'5″, 315), but it's a big jump in competition from Wayne State to the NFL. He's probably destined for the practice squad, but he still has a chance to make the roster.
Due to the depth the Dallas Cowboys have throughout the roster, it is extremely important the coaching staff gets things right when making cuts. All of the available spots are at a premium and I don't know if any of the undrafted free agents are good enough to claim one.