I don't think it matters who prepared them. It's under the purview of the minister. He can bring officials with him if he wishes, but my understanding of our system is that for the response from the government, the minister is responsible to the House and to the committee for the estimates.
This is brand new to me. It has been my experience in parliaments that the minister comes, and if he wants to bring the person who prepared those particular estimates to deal with the technicalities of it, then that's quite all right. But estimates have traditionally been an open-ended opportunity for questions to be asked of the minister on the department's activities.