I think there's a big difference between taking a month or two off to travel versus taking six months off to work in a bar. If I were hiring someone and that was their story I would think, "Why would this person leave their corporate job to stay up late at a mindless job working with a bunch of drunks? Is he going to quit on me too?"
Now I'm not denigrating people who work at bars, if I'm going to be all politically correct I should acknowledge that these jobs are probably stressful etc (I've been a bouncer and a bartender)... but my knee jerk reaction upon looking at a resume such as the one you may produce if you take the bartending job is, "This looks like a red flag." In general people think of bar's and nightclubs as having a certain lifestyle associated with them, and their might be a presumption that somebody who likes that lifestyle would be an unreliable employee.
I understand that doing the management part of the bar gig would actually be good experience and quite possibly much better experience than working at your day-job, but I think it may just complicate your resume, in general it's probably not good to have stuff on your resume that requires supplemental explanation, and a two month vacation before business school is probably quite common, a six-month period before b-school where the person took on a possibly-seemingly-random job would not be typical, and might get your resume passed over.