If a recipient marks my campaign as junk, will they be classified as bounced?

No, a contact is only classified as bounced when an email is not delivered. In most cases the bounceback message, which is viewable from Reports, will explain why it was not delivered.

On the other hand, when an email makes it to the junk folder (or spam folder, etc) it is regarded as being delivered so a bounceback message is not returned to us, and there is no real way to know that it was not delivered to an inbox.