I checked various sources on Jacob's footprints. They seem to have conclusively proved it was Jacob's footprint(s) because even Patty refers to them that way. IMO, they matched the shoe print in the driveway to one of Jacob's other similar shoes at home.
Here are some quotes about the prints:
"The police arrived six minutes later and went to the place where the boys had seen the man.
Jacobs footprints were on the driveway by where the man had been standing. But then they ended and his toe sort of dug into the gravel. There appeared to be some resistance at that point. There were tire tracks on the driveway. "
http://www.minnesotamonthly.com/media/Minnesota-Monthly/October-2009/Without-a-Trace/
"All that remained of him on the gravel road was a spot where Jacob's footprints seemed to show resistance. And then nothing."
http://abcnews.go.com/US/investigators-dig-evidence-wetterling-case-mom-hopeful/story?id=11075883
"On a gravel road was a spot where Jacob's footprints seemed to show resistance. And then...
"It's gone," Wetterling said. "It's just bizarre."
http://abcnews.go.com/Nightline/ElizabethVargas/jacob-wetterling-missing-20-years/story?id=8874577
"What rates as a nugget is a comment from WCCO's Don Shelby, who said that Patty Wetterling reminded him that Jacob's last footprint was leading into the driveway of the farm being searched Wednesday."
http://www.minnpost.com/glean/2010/07/lots-media-commotion-over-jacob-wetterling-story
"Sources tell WCCO the farm site is where they had found the last trace they could find of the eleven-year-old boy. Back in 1989, a police dog picked up Jacobs scent just inside the property and sources say it disappeared a couple hundred feet away. Sources also say a mold was made of Jacobs footprint on the site back then."
http://www.immelman.us/news/wetterling-suspect-dan-rassier/