The Ads displayed on your hubs are from Google so it is a requirement that you have an Adsense account to qualify. HP makes it easy to do so by going to your affiliate settings and selecting the appropriate option.
Adsense also pays you separately when someone clicks on your ads, so they need to be able to pay you so you will need the account for that. As you can see there are two ways to earn from Adsesne here on HubPages.
I would advise to sign up for the Adsense account as soon as possible so you can start earning.