PIT Bulletin 2005-04 states as follows:
Because the focus is on whether the amount is deducted from the employee's compensation, not on the type of plan to which it is contributed, an employer match should not be subject to Pennsylvania state tax.
That being said, at the federal level, the employer match to a 457(b) plan is subject to the $18,000 limit on total contributions. This contrasts with a 401(k) or 403(b) plan, in which only employee deferrals are subject to the $18,000 limit. Thus, if we're talking about a governmental 457(b) plan, it may make sense to have the employee deferrals made to the 457(b) plan, but the employer match made to a 401(a) plan. Of course, this doesn't work for a 457(b) plan of a nongovernmental employer.