Yes, maximum shear stress theory is applied but things are simplified in the Codes - Codes built for slide rules. If maximum shear stress is the radius of Mohr's circle, then "stress intensity" is the diameter. Why go through the trouble of dividing the diameter by two and the yield stress by two when you can just compare that stress intensity to yield? So, even though Appendix A may be based on yield stress (or other, lower limitatioins) Tresca Theory of failure (max shear) is applied.