I used them for buying Bit Coins, but that was a few months back. They seemed pretty straight foward on there account opening process, plus if I had any issues that couldn't be solved by phone. I could have visited there office considering there like an hour away. Even though as of right now I think there are some issues regarding people who were using the Dwolla services without properly registering as a money transfer service.
Since you mentioned it's for horse racing, my dad works at Plainridge and they take bets over the phone and knows all about that stuff. He and none of the guys working in the money room at the track have ever heard of it.