Is there a specific coefficient of friction required for a surface to be "slip resistant"? (ADAAG 4.5.1)

No. There are a variety of ways to measure the coefficient of friction for different materials and no single test device or procedure has been identified. A Board sponsored research project, described in the ADAAG Appendix Section A4.5.1, suggested some values but, without a defined test procedure, these recommendations cannot be applied.