Still haven't heard back from the "ask a CO" on this, so I might be proven wrong...
I understand the idea of doing everything you can to be 100% legal, but sometimes over-interpretation of the regs goes a little too far. I'm confident that the intention of the law in this case is simply to make sure that big game hunters wear a hat and a vest at minimum. Using another vest to cover your pack, blaze orange packs, etc., is just going above and beyond what is required. If you feel that if makes you even more safe, have at it.
Hunting is supposed to be enjoyable, don't get hung up on over-interpreting things. Read the regs and use common sense. There are so many gray areas when it comes to fish and game laws that if a CO was just out to lay a charge, he'll probably find something anyway.
Does anyone have any real examples of warnings or fines due to blaze orange being covered by a backpack? I've never heard of any, and we've run into a few in the field while deer or moose hunting with backpacks over vests.