That's actually a really interesting question. Can beginners tell who is doing good aikido or not? Any beginners out there wish to comment?
I guess I qualify (5 months of 2xweek plus a couple of courses, in addition to about 4/5 months a few years back) as a beginner. And I'd have to say that I do recognise good Aikido when I see it - and I've seen some very very good Aikido. That's not to say I have even the vaguest hint of a clue as to how to do some of it - that'll come in time.
I actually think it's more likely to be a problem the other way - when someone in hakama does bad Aikido. Even the best have off days, so what happens when someone is watching and suddenly 'It must be good Aikido - the person has hakama on..!'
Much less of a problem if everyone is wearing hakama..