My husband was scheduled to do this on one of our trips a few years back. It poured the morning of his drive, they were super nice and gave him a ride around the track in the van then drove him back to the BWI. Since it was near the end of our vacation he took a raincheck which he used at MIS (Michigan International Speedway). The Petty program was awesome, they even gave my kids and I a ride around the track in the van. DH loved it! And since he did it at MIS a 2 mile track he got up to higher speeds than they can at Disney as it is only 1 mile.
If you do it at Disney, schedule early in your trip in case of rain.