not an autograph hunter, but got my favorite, ken schrader, at wilmot speedway, during a rainout. i held up his motorcycle while he went and signed a local racers car!
prior to that i had taken a bunch of nascar buddies to their first dirt race at hales corners and they were amazed at the accessablity of the drivers, including schrader, after the races. i told them nascar drivers used to be that easy to talk to prior to big dollar sponsor commitments taking up all their time.
mid 80's at michigan, we ran into geoff bodine in frank's iga grocery at brooklyn, mi the saturday before the race. then we caught up with harry gant, driving himself to the track in a corvette, infield parking lot fence.
as far as tony stewart, i don't believe he's any different than any other driver. catch them when they aren't busy, and they will usually take the time for the fans. but act like an a$$ and try to intrude while they are busy, you should expect to get your head bit off.
anyway, i wish you well getting jimmie's autograph. last thought, some of the drivers make appearances at their souvenir trailers during the weekend. but expect a mob!