Will the auditor/consultant require full access to the SAP system?

Absolutely not! The auditor/consultant does not require, nor should they ever request, full access to the production system. In fact, they only require display access in order to perform the reviews involved in an SAP audit.

Some SAP default profiles (e.g. S_A.SHOW) can provide most of the display access necessary to use the SAP transactions required to perform their work. Where required, additional display access can be supplemented to the auditor/consultant user ID. A list of required access should be provided to the client prior to the audit start date to make the auditors/consultants time on site as efficient and productive as possible. Short answer is do not grant full SAP access to the auditor.