Yup, my employer (FAA) actually sent out a notice/warning about CBD oil. Short answer, don't use it. It makes sense to me...if they allow CBD use, someone could smoke pot and "mask" it by saying they are using CBD. Of course the levels would probably different but it clouds the water so to speak.
We get random screenings, either breathalyzer or urine.
Love how the OK law specifies an employee can't be terminated for usage... what about your aircraft mechanic, your neurosurgeon or your kids' bus driver? How do you feel about the uncertainty with knowing when and how much they use? But hey, Oklahomans voted for it, whether they read and understood the law and the consequences or not. lol
As SMS pointed out, the aviation industry is already federally regulated, and state law can't bind fed.gov. Similarly, I'm sure the various professional licensing agencies can step up: the hospital may not be able to fire you for using, but the board can suspend your license. I don't know what the license requirements are for school bus drivers, but I know truckers are federally regulated (including a medical exam, just like pilots).
I suspect the problem will sort itself out in time, just like with alcohol. As for the CBD oil making you pop hot, well, taking opioids will make you fail the test too, at which point you produce a copy of your valid prescription.
These are not intractable problems. There will be some teething, but nothing that can't be worked out (and we have more than a few example states to study and see what works).