Doug
OpenBadges currently defines the "recipient" of a badge only by an email address.
Mozilla's Backpack (the only one currently supported in Moodle) requires you to use Persona, their identity mechanism, which in turn is linked to an email account that it has validated. All the external backpacks I have seen so far require some sort of email address.
You can of course still issue badges to students in Moodle which will live on their Moodle profile in the Badges area without putting them in an external backpack at all.
I presume you are using some sort of made-up email for the Moodle accounts of students who have no real email address?
If so, be aware that when you issue a badge that it is valid only for that email address. Currently, Mozilla's Backpack will only allow you to upload a badge that was issued with the same email address as you are using for the backpack.
By default, Moodle uses the user's Moodle email address for a badge. But, if the user has connected their external backpack to Moodle (in Administration > My profile settings> Badges > My backpack settings > Email address) with a different address, it will use that one instead as the badge recipient.