I agree, innocent until proven guilty. Of course it is possible that wasn't Art playing, and I'd never claim that a replay alone is incontrovertible proof that it was, but I've been watching Art's Sim forever and that was textbook Sabin. In all the times I've seen Josh on streams down to his last match, I've never once seen him go to Sim to counterpick a Rog or any other character. Now Josh is a beast and I'd never say that he couldn't play Sim like that, but if I had to bet on whether it was Art or Josh in that particular match, I'm putting my money on Art.
Also, I find myself weighing potential cheating against "lolz online tourney", and I just can't muster up the gumption to give a fuck either way. It sucks for DeeDog since he can't prove he was cheated, but with this format you just have to accept the risk of lag and other hanky-panky.