No, the salary sacrifice calculation and income tax and National Insurance contribution saving are not affected.
However, if the employee is a higher or additional rate tax-payer and they were contributing to a personal or stakeholder pension they would pay their own contributions net of basic rate tax. They would then claim any higher and additional tax relief through their self-assessment tax return. As the contribution is now being paid by salary sacrifice (that is, by the employer) no income tax is deducted as the salary has been given up. So, they effectively get their tax relief immediately and do not have to claim it through their tax return.
If they are members of an occupational pension scheme, personal contributions are paid before income tax is deducted. There is no need to claim the higher and additional rate tax relief through their tax return. This is very similar to salary sacrifice but salary sacrifice also saves on National Insurance contributions.