can the wreckages of a hot air balloon and a hang glider be salvaged for a working hang glider?
To expand a bit on what @ratchetfreak said in a comment...  

The leading edge on that glider is not secured properly.  It would need to go around the bar all the way along the leading edge of the wing, otherwise the holes would make it so the airfoil doesn't function.  

As it is right now, the air would hit those gaps and make the cloth flutter, which would break up the airflow over the glider itself.  Thus you'd just have turbulence over the wing, which would make the wing stall.

So, yeah, in a nutshell, that wouldn't work as a glider as pictured above.

But, if he had found some string or wire from the wrecked balloon and properly secured some of the Hot Air Balloon cloth to the frame...  There's no reason it shouldn't work.  Hot Air Balloons are made out of fabric that is very very similar to what hang gliders are made from.