<i>Is he justified in asking for that?</i>
If the privilege is granted, yes. Otherwise, no.
Regardless, the consultant should have no difficulty in providing acceptable justification. He should know enough about what he’s doing to be able to explain — assuming that it’s actually required. And it might be.
A SAP implementation is no trivial task. It’s not unheard of to take many months. Even if not technically required, a lot of tasks may be done much sooner with high authority. If a longer implementation schedule is acceptable, things can be done the long way.
For example, a given important task might actually be done by a staff member who has the required authority. The consultant could take the extra time to provide necessary training and then perform any subsequent verification of proper task completion.