I'm accepting of ARed Gen. IV events because you can't tell them apart - technically even Gen. V. It's possible for people to say they are legit., but there is really no way to tell. (Note: there was a Shiny Eevee at Lv.50 there. It has an AR code. I've tested it and it works, but ATM any generations are still there. They get random stats like the event one did - AR lets you even check that in those games - so it's like an extension of the event.)
That's the same with cloning, too. I had only one Eevee with a 31/xx/31/31/31/31 spread and wanted to keep one in case I enter the event as well, so asked RNC to clone a couple. Since I have the nature covered by the Everstone anyway, my next bred Eevee with that spread would be identical anyway (except the specific Attack stat would differ). So, in the case of 6IVs especially, I just consider it a way of "speeding things up"; I got it once, I can get it again with or without cloning.
Shinies, on the other hand, are better for cloning. And no, you can't tell them apart, so I say there is a very good chance you could have a clone and not even know it. I have a Poké Ball Vivillon, too, but I can't fly to France; I was therefore accepting of a clone to get that one Dexed. I know it's legit. as it does not say June 4, which Power Saves I hear DOES have a hacked Wonder Card for.
Of course, in the case of the Eevee, I may breed another nature. Have to decide if I want to spend time evolving one tomorrow, then enter it for the contest.