Privacy of Historical Data

Our ERP Implementation Consultant is insisting on a point which is in our opinion against the privacy of the companies real time historical data. The management is not willing to permit him or any consultant to view our historical data (such as , item master, price lists, costing details etc). The management is prepared to generate test data in as much qty as may be required by the consultant. But the consultant insists that he must have superuser accesses for all three environments i.e. (Dev, QA & Production) until the very day of Go-Live . Is he justified in asking for that?