I don't recall seeing both in the backfield at the same time. I think the Cowboys could have great success with this formation: 2 RBs (Zeke and Pollard), 1 TE (Jarwin or Witten) and 2 WRs (Cooper and Cobb). I am guessing defenses would have to counter with 5 DBs. Defenses would have to account for two RBs who can both run and catch on both sides of the field and would also have to guard the middle of the field since both RBs can run inside too. Defenses would need to account for both RBs going out in the flat or screens. Might be able to get some explosive players in advantageous one-on-one matchups. Would like to see them try this sometime.