The IRS says yes to 457B plans. Link: https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-savings-contributions-cred...

"Depending on your adjusted gross income reported on your Form 1040 series return, the amount of the credit is 50%, 20% or 10% of:

• contributions you make to a traditional or Roth IRA,
• elective salary deferral contributions to a 401(k), 403(b), governmental 457(b), SARSEP, or SIMPLE plan,
• voluntary after-tax employee contributions made to a qualified retirement plan (including the federal Thrift Savings Plan) or 403(b) plan,
• contributions to a 501(c)(18)(D) plan, or
• contributions made to an ABLE account for which you are the designated beneficiary (beginning in 2018)."
• This is what the IRS says about 457B plans. 

       "Plans of deferred compensation described in IRC section 457 are available for certain state and local governments and non-governmental entities tax exempt under IRC Section 501. They can be either eligible plans under IRC 457(b) or ineligible plans under IRC 457(f). Plans eligible under 457(b) allow employees of sponsoring organizations to defer income taxation on retirement savings into future years. Ineligible plans may trigger different tax treatment under IRC 457(f)."

• Seems like an error in ProSeries to me