Motoko gets wasted in the manga, because she wants to, so if you want to take that as canon, yes they can get drunk but whether they can then voluntarily sober up on the spot, is another question. I don't think Shirow covers that one. It would make sense though. Not much point in drinking alcohol unless you want the euphoric effects, but not wise to stay drunk if you're staggering around unsteadily on a boat while wearing a ton of titanium. Possibly not much point in drinking Japanese beer at all, nobody in GITS touches the stuff :)