Yeah, it would -- unless you changed the date to when it was an official event then caught it, nobody would know. But if you caught it with a recent date, they'd know that it wasn't legit (depending on your opinion on legit).
Some people would be okay that you hacked the pass but not the Pokemon, as they only consider hacked 'mons to be "illegal". Others prefer that you get it 100% honestly. It just depends. But if it's fine with you and you're not trading it or anything, then whatever you want goes.