Sillograph:
Not true, my friend.
The CPL comes into the business with a MECIR, covering most multi engine aircraft under 5700kgs. So he / she has the CPL licence, and the ME IFR rating.
So any training done by the CP is done to bring CPL up to the company standard on a particular aircraft eg from the Duchess or Baron to a 402 - all ME. This training doesn't relate to the issue of a licence or rating.
As such, for this, the CP does not require an instructor's rating.