PN,
I have to admit that my RFA time was pre the Captain Calamity saga, but we often had whole crew quiz nights, flight deck BBQs etc where I saw representatives of the whole crew enjoying "down time". There was probably a "bottle to throttle" equivalent for bridge/engineering watchkeepers. (like I said, common sense)
At the time the RFA Doctor would control and administer the tests as requested by the command when a breach was suspected.
If the merchant rules have changed again since, I am happy to be corrected.
Being ex RN I know ALL crew members on RN ships can drink (off watch) which is why I think the testing will be a positive thing.