So what is the difference between this ICMA sense of yielding, in the context of, I guess, push-hands, and just "taking the ukemi"properly?
As Carsten noted, where this is yin there is also yang. When we are neutralizing, we should also entering, not before or after, but rather simultaneously. The neutralization is the entry. Irimi-tenkan.
To bring up a really tired example from the past: imagine a T-shaped peg driven into the ground that can freely swivel. Push on one arm of the T and it receives, and the other one... it issues. Yin and yang. Push on the center of the peg, and there is still... yin and yang, even at the same point of contact.
Not yin, then yang, nor yang, then yin. Yin AND yang, together.
But, if this is the "proper" way to take ukemi, count me in.