As long as the wind puts more torque on the prop than it does drag on the vehicle, it will accelerate, even if that's directly into the wind that's spinning the prop. No reason a prop can't rotate while facing into the wind. Think of those classic
pond-pumping windmills in farming regions with vanes on the back to automatically keep their prop facing into the wind.
Blackbird isn't using its prop for thrust from accelerating air backwards; it's got a mechanical linkage between the prop shaft and the wheels. It's a windmill on wheels, rather than an airplane without wings, turning a wheel to move rather than turning a wheel to grind grain (or whatever other work you built the windmill to do).