I know American and Delta fly in there but they are CRAF missions. I'm not sure if normal jumpseat privledges apply since it's a government contract. My guess would be no jumpseaters due to the nature of the flights (ie...troop movement).
No U.S. air carriers fly scheduled service into OKBK except Kalitta. Sometime Evergreen flys in there but they've been going to Baghdad direct more than into Kuwait. You will always see U.S. carriers on the ramp but these are military CRAF flights and nobody but the military gets access to these flights.
The best way to get to Kuwait is to buy an ID90 or Zone fare on KLM AF or LF. The Air France flight seems to be the best in terms of loads because they fly an A320 long range to Kuwait so they don't market their flights there like the wide-body trips do. KLM is 90% U.S. military in the cabin so expect that flight to be full. B.A. is also usually full.
You can also fly to DXB or BAH and ID into OKBK on EK or GF. As far as a visa is concerned, Americans can get visas on arrival in Kuwait. Not sure why anyone would want to go there though, except on business. Miserable place.
Whymeworry is right with fligth info. All the US carriers that go have nothing but troops and unless you work that carrier doing the flight, you will not get on. But I do have to say the best thing about Q8 is that the price of gold is great!!! I been there many, many times and you can not touch the price of gold and hand made suites in the US for what you pay there. Got a killer tan as welll over the summer.