I've been on development teams which had contractors as 20% or more members. We had just couple of interviews and next-day offers for contractors while full timers went through multi-month process. Both worked on same code, often similarly complex tasks and used same on-boarding docs etc. One difference was that full timers were given more longer term tasks although, looking back, I feel many longer tasks simply became longer term because of tribal knowledge full timers developed and kept to themselves. The contractors were required to extensively document everything all the time :).