There's been smallish backs who've gotten it done in the past. Warrick Dunn was 5'8 176lbs coming out and played in the NFL for 12 seasons missing only 12 career games. As one might expect he wasn't a TD machine as a small RB and only scored 49 career TDs yet averaged an outstanding 913 yards over those years, had 8 TDs over 50 yards, averaged 42 receptions a season, and had 15 receiving TDs. Dunn was a much faster back, but he wasn't built much differently save a couple inches and Tampa and Atlanta both made sure he didn't carry the ball but about 14 times a game.
Phillip Lindsay 5'8 190lbs is another smallish player who had limited success in the NFL. Yes both Lindsay and Dunn had a few inches on Vaughn, but we're talking about a depth running back here, not a wide receiver. Lindsay carved out a couple of really good seasons before his body size betrayed him. That said he averaged 4.95 a carry, scored 16 TDs, and 2048 yards in his first two seasons. Then yes, his size caught up with him.
Good football players who are coached correctly and put in the right situations can be effective at any size. I don't know that Deuce will even make the team, but I don't think it will have to do with his size if he doesn't. He's short not little, has gotten it done against bigger players at every level he's played, and plays a position where size might mean the very least.