Interesting point on the hackle collar, and to be honest I have not given the idea much thought up until this point. I would imagine that it is a combination of the reasons you outlined.
On your question, yes, Mr. Brislain indicated that it should be tied with a picked out body in his tying instructions for this fly. And I like a picked out shaggy body myself. I do have his book on Salmon bugs and must agree. Good stuff.
Great story, I have never met him myself.