I did an endurance last night (Indy 500) and they are definitely earning different amounts of EXP.
1st Driver: 11.80 -> 19.55
2nd Driver: 11.80 -> 19.50
3rd Driver: 11.80 -> 18.85
4th Driver: 11.80 -> 17.25
1st, 2nd and 3rd drivers had blue arrows. 4th driver had a green arrow.
They were also driving in the order that I have listed them in.
I wasn't watching the entire race, but it looked like they had to pit every 30th lap.
0 - 30: 1st Driver
31 - 60: 2nd Driver
61 - 90: 3rd Driver
91 - 120: 4th Driver
121 - 150: 1st Driver
151 - 180: 2nd Driver
181 - 200: 3rd Driver