My 5 Pence worth.....
Went to Simcom in Orlando in July this year to do an FAA ATP flight test (already had the written) and a J41 type rating on the FAA licence - both in a sim. I`m British, and apart from the pain-in-the-arse TSA approval and fingerprinting at Flightsafety in Farnborough, all I did visa wise,was fill in the standard visa-waiver (ESTA). At Orlando I was asked by both Immigration and Customs what I was going to be doing there and I quite truthfully said I was there for Simulator training and they had no problem with that. Simcom seemed only to be interested that I had the TSA approval-that was very important to them, but they were'nt at all interested in what visa I had.
By the way this isn`t the first time I've done this - I`ve been going to the States for over ten years for sim training for various things - all on the visa-waiver...
Thats just my experience.
Regards