bafanguy
The biggest company (that I'm aware of) dealing with "first officer courses" or "pay to fly revenue trips" is (if I'm not mistaking) American and is called Eagle jet. They place unexperienced pilots who have saved a lot of money or are fortunate enough to have rich dads, with companies like Ameriflight and other 135 operators. Other american companies that has similar buissnes ideas is Central air, Alpine air and a bunch of other smaller 135 operators in the states. Eaglejet places 220h guys with a typerating with foreign companies as well. Flying anything from c182 to A-330.
So, to answer you question. I think they are just hired as any other short term contract pilots. Only difference beeing that these guys are extremely unexperienced to be contract pilots and they will probably leave when they have achieved only the knowledge required to operate the specific type in an normal, non eventfull, daly operation. That is all the airlines is asking for nowadays. I think it is the same in the states and in europe, but the companies I have heard about that does this is mainly based in "second world Europe", Africa or Asia.
/bb