Does the observer display all events in the voting area or is it possible to associate an observer with a specific event?

Eligo allows both options. If the observer is added without specifying an event, they see them all, otherwise if the event(s) has already been created you can restrict visibility to that event(s) when you create the user. 

For more details, we suggest you read the following article: 

• Observer: What it is and how it works