According to the IRS, mandatory employee contributions to state disability insurance, such as California SDI, are included in "state and local income taxes" that federal taxpayers who itemize on Schedule A can choose to deduct.
Meanwhile, California specifies that if an employer pays SDI for an employee (as distinct from withholding which merely facilitates the employee's payment of it),
the employee's wages increase by the amount of ... SDI paid. ... This amount ... should be included on the Form W-2, and should be reported by the employee as taxable income ... Also, the SDI paid by the employer should be shown on the Form W-2 as though the SDI amounts were actually withheld from the employee's pay.
This indicates that the amount paid directly "employer -> state" is treated as if it were paid "employer -> employee -> state" (i.e., like the normal case of withholding). Both the letter and the spirit of these rules seem to imply that the employee, as a federal taxpayer, will be imputed with additional income and an offsetting deduction (if itemizing state and local income taxes). This makes sense as taxes "should" be indifferent to mere labeling, e.g., if the employer simply gave a raise in lieu of paying SDI (in which case both the income and the deduction for the employee are clear).
Is there a source that explicitly confirms whether the federal deduction applies for employees in the case of SDI (California in particular) that is paid by the employer and imputed as income to the employee on the W-2?