As it relates to the first recommendation, it's simply putting in a policy statement that workers ought not to come to work under the influence of cannabis or other drugs without a medical authorization or prescription, which answers one of your questions, and without employer approval.
Certainly, in non safety sensitive positions, there is a lower worry about it affecting safety. It might affect productivity, and I'm sure it does, but that's a different problem, which the employers will have to deal with. I think the point behind the first recommendation is that it's more of a symbolic statement to say to employers and to workers that it's not a good idea to come to work when they're not sober, but if they're under the influence of a prescription drug, that's fine. They should report discreetly to the HR department. They'll have to keep it confidential, but if the person has some sort of medical reaction, they're at least aware. Many employers have a policy that reflects what I'm suggesting, but it's certainly not the law.
I don't think the health and welfare concern this represents for workers and their safety is a hammer. It's more like a gentle net to catch the fly and set it free.