Both are actors on the film, neither of them are producers for the film. The producer's list at imdb.com:
Produced by
Robin Bissell .... executive producer
Suzanne Collins .... executive producer
Chantal Feghali .... co-executive producer
Nina Jacobson .... producer
Jon Kilik .... producer
Aldric La’auli Porter .... co-producer
Louise Rosner .... executive producer
Bryan Unkeless .... co-producer
You’re right. I misread a credits list earlier. Harrelson and Kravitz are actors in it, not producers.
BTW, here is a review by the socialists over at Socialist Worker magazine:
http://socialistworker.org/2012/01/26/hope-and-the-hunger-games
Naturally they love it.