You can maintain the Partner data in Equipment Master through Partner Functions.
If not, you can maintain the Employee name in short text of the Measurement document.
Instead of doing that in excel, details can be retrieved from SAP. But there won't be any integration between this Measurement document value & deductions to be done in payroll.
You can refer below document for assigning the employee to vehicles through Partner functions.
Partner Determination Procedure - Overview
Hope, simultaneously one vehicle will not be used by more than one employee.
If 1 Employee : 1 Vehicle, then use Partner function to get the personal usage & official usage by having only 2 valuation codes instead of having employee wise codes as employee are more dynamic.
If n Employee : 1 Vehicle, then use Short text in Measurement document to mention the employee details with same 2 valuation codes.