Sure, it's risky, keeping two. But every team has to play the 53-man, 45-dressing game. Their choice was to keep another position player on the active roster until Lynch returns. When Shaud Williams was the 3rd rb - how much action did he see?
It's a dice roll, but personally if I were calling the shots, I'd do what they did - they have some thinness and question marks at other spots.
There's many ways to slice up the roster - CIN chose to keep both DD Dorsey and Brian Leonard, and only 1 FB. Dorsey and Leonard both did well in pre-season, and Dorsey showed ST flashes. They have a 2 week exemption for that whale they drafted in the #6 spot, but I think they will keep Dorsey on the team.
In any event, it's time to coach and play the players you have. Time to park the "what ifs?" Go with what you got...