Sin, yes. But not inherently evil from the start (neither Satan nor Connor nor the pre-zombie DeRosa).
De Rosa was a human being. In the first draft, all Satan needed to create zombie-De Rosa was his DNA, so the original DNA source could still be alive. In the next draft, it's a little more sensible. Satan (and the demons helping him) enter the body of a dead man and make it seem that he's alive. I'm fact, I could make it so that it always requires multiple demons to animate a dead man. That would explain how they do it (ie one demon can't by itself).
Since Connor is not inherently evil and Satan does not provide any satanic DNA (there's no such thing), the best Satan can do is manipulate Connor's genes (inherited from the zombie at conception) to give him his superpowers. Granted, there are genes that make humans do all kinds of evil things (eg murderous psychopath), but that makes those humans too unpredictable for Satan. One thing Satan could definitely change through DNA is the way that some animals attach themselves on to another animal as their perceived parent. That's how he could make Connor love him, virtually unconditionally.
I didn't want to go down the route of Connor's powers being spiritual because I consider that a cop out from a storyteller's perspective (eg Connor needs powers, so Satan "somehow" passed on his spiritual powers, but we can't explain how. Yuck.). I think a DNA-based solution is closer to something we can understand and relate to. For example, think about all the powers that other animals have that we don't (gorilla strength, incredible speed, ability to breathe under water, ability to fly, ability to use the Earth's magnetic field for navigation, etc.). Is it such a stretch then to imagine Connor could draw lightning from the sky? Just carry a lot of metal in a thunderstorm, and you can do it too. 
The Bible says that Satan gave the Antichrist his power, throne, and authority (some wording like that), but Satan would never share power with someone he didn't trust absolutely, hence for me, it had to be a son. That made it obvious that Connor's powers should come from his genes.
Also, remember Connor is actually more powerful than Satan (although Satan doesn't know that yet) since Satan has only spiritual powers, whereas Connor is a form of hybrid with superhuman DNA. So, I'm free to decide that Connor is stronger.
I'm beginning to ramble, so I'll stop there.