Thanks for reply, JohnPM.
I have two cases.
In one, hatches have boundaries, but they are in different layer. Does this matter? If yes, I will move them to same layer.
In other case, unfortunately I have no boundaries. I found this to recreate boundaries:
http://www.jtbworld.com/lisp/hatchb.htm
But, after exporting result of this script, I have problems with islands, as mentioned before.
Is there any "proper" way to recreate inner and outer boundaries from ONLY hatches?