I don't know if takeoff would be the right term, but the wing should generate lift with any headwind.
The ultralight could takeoff with a strong enough headwind, but would be blown away in the process. This would not only be..ahem...very dangerous, but would cause the ultralight to lose a lot of airspeed. If it were tethered to the ground, it would fly like a kite. The wind would pick it up, and the strings or rope would prevent it from losing control or flying away.