I use Google Apps and my email is configured to use Inbox. My default delivery address is set to nobody@example.com, and my primary account @example.com has been granted access by delegation. I've successfully used this from the Gmail interface, but I have no idea how to do it from the Inbox UI.
Oddly, using Google to search for this has been significantly difficult, thanks to the generic terms.
Best Answer
As of this writing (October 2015) there is no way to access a delegated mailbox from Inbox for Google without switching back to Gmail. Navigate to mail.google.com and use the delegated mailbox from that UI.