Questions like these make my head hurt and make me happy that the Army requires two pilots in our King Airs.
On the "is this a good idea" question, I would say this is a great learning opportunity and a great opportunity for a full time PIC job, but doesn't have to be the only way the student gains his flight experience. Any time spent in the front seat of a King Air, whether you are logging time or not, will be time well spent learning about complicated multi-engine IFR operations. That's coming from an 1800 hour King Air guy.
What is there to say this guy can't sit right seat from time to time and also get a job instructing elsewhere?