Hello.
1. If the thing that you make can be called a tool, like it can be re-used to make many games and is not specific to this one, then yes, it is fine to develop tools before the start of the jam. Essentially in your example, you would be making the functionality that something like Adventure Game Studio or Adventure Creator provide, and since it is fine to use those products, it is also fine to create your own similar tools before the jam as well.
2. Yes, it can certainly have sub-genres. The requirement is that it be clearly and primarily an adventure game, but sub-genres are fine.
Welcome aboard!