I used to organize reenactments and the costs are extremely high. I think this is a novel idea and helps defray the costs away from participants and the spectators. For instance, the liability insurance alone for a small reenactment of roughly 1000 reenactors fifteen years ago was $12,000. I will never organize another reenactment, the time involved was too much for one that has a real job.
I was a little unsure about corporations getting involved with re-enacting. As you said, it can be very expensive. In know in FL, the high costs and payouts have caused considerable controversy (over films, rights, etc.).
I just hope the reenactors don't sport Nike shoes and Wrangler jeans. Let's hope it doesn't get as flashy as nascar : )
One more thing, corporations' job is to make money, very little is done just for "charity" - I'm sure they will reap rewards for this.