No, not in standard lineups other than in a flex spot. There are specific special competitions, though, that do use these types of positions.
Yes, it is just dependent on the competition you choose to participate in.
Yes, depending on the site/app and the competition you select to participate in?
Daily fantasy is legal in pretty much the entire United States. Six states currently don’t allow it but don’t worry; the site/app will use your location to determine your eligibility.