According to our FOM (Flight Ops Manual), the Gateways are:

Gateway 1 - the normal process
Gateway 2 - Bluedarts (basically guaranteed interviews for anyone who gets a Bluedart from a Jetblue pilot)
Gateway 3 to 5 - for internals
Gateway 6 - university gateway - which is for graduates of AABI schools who go through the process and work at CapeAir (and I'm hearing rumors about Expressjet)