yeah, the only problems it could cause, is if you rely on the orientation of the mesh in code, but i suggest never doing that, and using socket transforms instead.
maybe it could cause some kind of gimbal lock, but if you are rotating a mesh in odd enough ways to cause gimbal lock, you should probably be using quaternions, instead of Euler angles. given that this engine is designed for first person shooters, the order they multiply matrices probably relies on the idea that most things wont roll, and most things rotate in yaw more than pitch, so starting with a messed up yaw offset should be the least likely axis to cause gimbal lock.
but i agree, i would love to hear from Epic staff, why they don’t follow their own content standards with their example content. i have a feeling that its because their rigging software makes axis assumptions for bone/pose mirroring in Maya, but that’s just a guess.