Is there a way to hide the suburb on a listing

Hello yukino. You can't I'm sorry. Suburb is a required field when you make the listing. 

All you can do is explain in the description or title if it operates across multiple suburbs. 

So what happens where there is no suburb at all that the business is related to. It could be a nationwide online business with no physical location at all

You have to select a location. You can't progress and create your listing otherwise. Every business has to have a point of contact location at the least. Even if they are entirely online.