I'm probably one of the few people here who doesn't think DR is involved (at least not directly). I still strongly lean towards a vehicle being at or near the scene. The boys may not have seen or heard a vehicle, but it was dark out, and once the boys realized what kind of situation they were in, I wouldn't expect them to notice anything else going on around them.
I'm also on the fence about Kevin's tire tracks. If I'm understanding it correctly, Kevin came forward and told them the tracks were his. How did they verify the tracks were his? By Kevin's word only? I don't necessarily doubt that he drove up the driveway, but I'd have more faith that they were his tracks if they were actually able to compare his tire tracks from the vehicle he was driving at the time to the tracks that were in question on the driveway. However, this doesn't seem like much of a possibility if he no longer had possession of the vehicle and/or tires by the time he came forward.
Also, if those tracks belonged to DR (as this has been suggested here on WS), wouldn't they have been able to identify the vehicle?
Regardless if the tracks were made by Kevin's vehicle, DR's vehicle, or someone else's vehicle, Jacob's prints and scent ended next to them and his toe dug into the dirt. In my opinion, Jacob was taken away in a vehicle. I have a hard time believing Jacob is on the farm. I'm not even convinced that he's no longer alive. We've seen numerous long term missing children come home in the last few years. I know it's still probably a small percentage, but I don't think it's impossible for Jacob, especially since they have no evidence indicating otherwise.
Let's not forget that the scene did not seem to be completely secured immediately afterwards, either. My personal opinion on why that seems to be the case is that everyone was just expecting to find Jacob immediately and didn't think this was going to be a long term case. Twenty-five years later and still no answers. Who could have possibly imagined?