Don't know about other tracks, but at Derwent Park the marshals have the straight forward description of "flagman/raker". IE - if the referee puts the red lights on, you put the flag out; and inbetween races you rake the boards.
There isn't much incident work - if there's a faller who doesn't sort themselves out the reds will come on and the medical teams will beat you there. At least I normally do
Still, being on the inside of the track is the less dusty place to watch the action, if slightly dizzy...