But I see no reason why the drag from the wheels isn't exactly canceling out the benefit of rotating the propeller.
The Energy generated from the wheels has to match the Energy lost by the propeller. Thanks to gearing, the force is not the same.
Energy isn't the problem, a decent sized windmill can generate a megawatt of power. And it can generate the energy perpetually (assuming perpetual wind).
Consider if the vehicle was stationary, then we could easily generate the power from the wind: the force against the wheels wouldn't lose us any energy because E=mv^2 and so dE/dv=0 when v=0. Now imagine we are travelling at exactly the speed of the wind. Then our velocity relative to the wind is 0 so dE/dv=0. Thus we can push against wind without losing any energy, the same way a stationary windmill can push against the ground without losing energy. And so we can generate energy from the ground speed without losing kinetic energy (ignoring for the moment that the propeller doesn't have perfect grip on the air)
So we are currently travelling at wind speed, and generating energy from the ground. We now use that energy to push against the the wind to make us go even faster. Note that even a 50KW engine feels powerful when we are going slow and in first gear, and even a 200KWH engine can't burn rubber when we are going at 100KM/h. This comes back to E=mv^2, because Energy is proportional to the square of the Velocity, it takes more energy to speed up the faster we are going.
Note that we are still travelling faster relative to the ground than the air. Thus we can use the same trick as gears in an engine, we use a high gear relative the ground so have only a small force. We use a low gear relative to the air so we generate more force (for the same energy). We continue to speed up until the energy we gain from the different gearing ceases to make up for friction and other inefficiencies in the system (such as the propeller not having perfect grip on the air).