Nope! You can give Credit to anyone at any time. If a person is not already on Credly, all you need is their email address to give them Credit. Or, if you are signed in using your Facebook or LinkedIn account, you can give Credit to any of your contacts on either service.
When you send someone a Credit, they will receive an email notification and from there they can either sign in to accept the Credit or easily create a new account if they are new to Credly. Either way, the credit you sent them will be waiting for them to accept when the next login with an account that they have associated with the email address you used to issue the Credit.
When using the Credly mobile app you can also give credit to anyone who checks into events you create or manage.