Currently, Google allows to create a Hangout via 3rd party apps, like drupe, only with contacts who have G+ accounts. That is because Google does allow you to sync your G+ contacts with your local address book contacts (which drupe's available contact list is drawn from), but it doesn't allow syncing the Hangouts contacts. That's just how they roll.
To allow using Hangouts with people from your G+ circles: Open your Google+ > Settings > Account > Contacts > Keep contacts up to date.