Employer reimbursements
If the reimbursements were under an accountable plan, then they would not be income to you and the employer would should not withhold taxes. However, if the reimbursements were not under an accountable plan, then they are income to you, they are treated as salary, and the employer must withhold tax.
However, if it is treated as income to you, you can deduct the expenses of moving, etc. as an employee business expense.