It depends. This is the first material I have heard of that would allow you to have structural elements lighter than air. Just an empty envelope is not very rigid.
A foam structure could yield lower release speed in case of puncture, and possibly prevent explosive fire propagation in hydrogen, thus allowing its safe use in airships (modern "cold air" airships use the rarer and more expensive helium instead)
Yes. The only reason I can think of that you would do this is to build some kind of hybrid airship that generated some lift from wings to increase MTOW (lifting capacity) but still has all the energy efficiency of low speed and therefore low drag.
