Well, I might sound like a horrible person, but I'd still report them, with the possible exception of long TO (like in between sessions) where they shouldn't be drinking on the grounds, per se, but there are no kids around nor will be for some time. (In which case they'd get a warning and next time I'd report them).
I just have no tolerance for drinking in those situations, even if it was my best friend. I invited a bunch of people over for a movie marathon, and I put in the invite that while they could bring and drink their own alcohol (which is an improvement for me, since normally I host dry functions), that if they had any alcohol at all and then attempted to drive, I would disown them as a friend. And I mean it. Any amount of alcohol affects your judgement, even if only a little. There is no reason why you need to drink on your TO, period. And if you do, that's a problem you need look into further, and maybe getting fired from a camping job will help you to see that.
I know I must sound like a total bitch, but I don't care. With the way things can go wrong at camp, you need people to be at their best. Besides, we're always talking campers coming first, right? How do you think it would be for a little girl who's dad is alcoholic, and has camp as her only escape from a broken home life, to smell the faint waftings of beer on a counselor?