If it happens, it's Dorion exerting leverage. Dallas needs NHL D right now, and a historical amount of teams (at least in the East) are fighting for playoff spots. I could imagine that might depress the market in terms of NHL defenders being available.
I agree about your assessment of Wideman's value. But Dorion has to want to move him right now for that kind of pick for it to happen. He may very well understand the leverage he has against Dallas and thus is asking for an overpayment.
Dorion can hold on to Wideman until the deadline, benefit from the depth, and still get a mid round pick. Jim Nill has failed to make the playoffs consistently, now a huge chunk of his D are hurt, and the market might be a seller's market anyways due to the amount of teams still in the running for playoffs. Maybe we don't get Hintz, but if Dallas acquires a D, I think we'll see an overpayment from them.