This is probably not that rare.
This.
You shouldn't be stoned on the job, at any job, but this certainly isn't shocking news.
I would say it's exceptionally common.
A couple times here in Seattle I'd wait outside the Key Arena players exit after the game with kids. SOmetimes the players would stop their cars on their way out to sign a few autographs.
One time Jelani McCoy pulled out in an SUV... opened his window and tons of smoke came streaming out. Desmond Mason was laying down in the back seat.
I think most of them smoke weed. Also, in the mid 90s a couple different people told me that Sam Perkins smoked crack at Gary Payton's house. I assumed it was just a rumor... and then later Shawn Kemp was caught with crack... so it made the whole Perkins thing a lot more plausible.