Only unlike Team-Fortress, none of the choices are crippled. Your character can still use any weapon and is adept at fighting as normal. Each job adds a special ability or two that is useful for Onslaught play.  Your job choices are as follows:

Courier - The Courier can drive any vehicle at 125% of its normal speed. He also runs faster than the other characters. This is who you want to get tanks to where they need to be.

Node Tender - The Node Tender has an unlimited supply of Link ammo, and heals & builds nodes faster than average.  This makes him a stellar defender.

Mechanic - The Mechanic repairs damaged vehicles twice as fast as normal, using half as much Link ammo. He can also steal locked enemy vehicles, given a short amount of time.

Warrior - The best at combat, the Warrior spawns with 100 armor and every weapon that's available on the map. (Except for Super-weapons)

Pilot - A natural with the Raptor and Cicada, his maneuverability is superior with both. He also has a parachute; letting him take very little damage from falling. We use the Chute Mutator for this purpose.

Defender - The Defender is tops at holding nodes. He spawns with extra armor and the Avril. He can also teleport to friendly nodes that are under attack.

Berserker - Whether with Rockets, Grenades, Flak, or even Super-weapons, the Berserker never causes himself any splash damage. He also regenerates health slowly. Go nuts.

When first joining a server, a player is presented with a menu, where he can press 1-7 to choose a job. Viewing the scoreboard lets you see what jobs your teammates have already chosen. At any time, you can choose a new job, but it will not take effect until you have died and re-spawned.