UTSW makes a strong point...if you can drink in a mature & responsbiel fashion AND the others were drinking first (I would certainly NOT initiate it), a drink or two - determined by your own limits of consumption - should be OK. However, with most all of these interview associated dinners, even if the attendings are not present - usually they are not, the residents fill out evaluations on you. The folks with whom you choose to party are not always the same folks you would prefer to work looooong hours with day & night...bear that in mind, please.
Lastly, and this is only second hand info, I met a lady fom U MI on the interview trail - in Richmond, I believe. She forewarned me of a program where the residents & attendings all went out to dinner with loads of alcohol, if you wanted it, for free. But, the next day, al of those who chose to party-hardy were intensively interogated about their partying/drinking habits. This person got bad vibes from the situation and stayed conservative...besides, she said the program was undewhelming too, and did not get the third degree. But, she heard several fo the others lamenting what had happend.
Sorry, I cannot honestly recall which program it was...I would love to think that this was an urban legend, so to speak. However, you just never know.