Maphacking exists, but likely isn't as widespread as people like to think. In 6 years of playing CoH1, I never once was sure I was facing a maphacker, and only rarely was I ever suspicious. Even then, going back and watching the replay usually removed any suspicion I had. But people like to have something they can blame for their losses, and maphacking is the perfect scapegoat for that.
Indeed I wached many of replies and change my mind after waching them, as you say, in some cases. In other cases though, I kept my opinion it's maphack. I know, I know, I should submit this to Relic. Did that in COH1, did it in COH2. Nothing happened. One time same player was reported by someone else too, but still nothing.
I don't know if Relic realy cares much about hacking. My guess is they don't. They don't care much about bugs or optimization since they prioritize the new faction and new content compared to other things that are the game's base, how could we expect they will invest much to protect us from cheaters? The phenomenon is not as spread as in COH1, but it surely exists in a bothering quantity in COH2 too.
I tried maphack in vCOH for a while and nothing happened to me. I was winning left and right and nobody punished me. Besides seeing everything, you had warning signs for camo units, mines, incoming arty and off-map strikes. Nothing could surprise you, you knew everything before it happened. A total bullshit, it made me sick and I quit after 1 month. So if an idiot is playing against me, it could easily wreck me in a competitive match if such feature exists in COH2. And guess what? THAT HACK WAS FREE. And you wanna make me believe Relic did much against this in COH2? I doubt. The only thing annoying for hackers and their clients were the constant montly patches that changed some game files and the filty hacks didn't work anymore, so they had to work again. Haven't you notice that the gameplay is "cleaner" 2 - 3 weeks after each patch? Even best players - though they finally win - are making mistakes. Then, some idiots appear from nowhere with smurf acounts or not, they show you through their build orders and the way they are losing squads that they are shitty at this game, still they know everything you have, where you have it and where your mgs, packs etc are faced to. And so on.
I played COH1 for 5-6 years. I'm playing COH2 since it was released. I think I can tell if someone is hacking or not.