My D does not have FICA withheld from her university “student employment” job (non federal work-study job on campus).
https://www.irs.gov/charities-non-profits/student-exception-to-fica-tax
But it is true that federal work-study earnings are subtracted from total student income on FAFSA.
But if income is below FAFSA student income protection allowance ($6,660 for 2019/20 FAFSA), it wouldn’t affect EFC either.