This has been my understanding for some time. I believe the national forests didn't have the resources to fight the lawsuit with ursack so they wrote vague requirements without specifying actual acceptable equipment. I take it to mean they don't want you to use the ursack but if you throw a big enough stink they will allow it.

The problem is, if you hike in from the eastern side of the Sierra's I think Inyo NF stops around the pass then your into a different jurisdiction that may not allow ursack.