Yeah, it's a pretty common policy in physical jobs in the places I've lived. Any accident results in a drug test.
My old hospital didn't test unless someone was suspected of using, but the company I work for now does during the pre-employment process and then randomly. If there's an incident or suspicion, everyone gets tested. During random testing, they can select anyone, including the doctors. If someone doesn't want to give up a habit, they need to be careful to look for an employer who doesn't test.
Between these two hospitals, I've seen one person fired for being drunk on the job (confirmed by breathalyzer), another for pot, and a third for pot and a possible opiate positive. And I think one of the reasons they've been taking it more seriously is the growing problem with theft of controlled drugs. I'm not suggesting that smoking pot makes people steal midaz and ketamine (it doesn't!), but employers are limited in what they can do to keep things under control.
Right, that's one of the problems. There's no guideline to define impairment like there is with alcohol. If someone pops on a simple pee test, all you know is that they used pot at some point fairly recently. It could've been that morning or it could've been two days ago, and all you have is that person's word to go on. No employer or school is going to just take someone's word for it if they consider drug use on the job to be a violation of policy. The only thing that would really change the way it works is a cheap, quick test that measures precisely how much THC you have in your system and a guideline that tells you approximately what that means as to how impaired someone is.
Even if/when it becomes legal, there's no telling whether any specific agency or school or employer's policy is going to change.
As for the DEA license, have they become stricter in recent years? A coworker of mine once worked with a doctor who got caught dealing ketamine. We looked him up on the state licensing board's website, since they listed charges, disciplinary actions, etc. as a matter of public record. It was about 10 years ago now, and he merely had his license suspended. I found it pretty shocking that they didn't revoke it out right. He was literally dealing drugs. Was this a bizarre one-in-a-million got-off-easy situation? Or did it used to be a little different?