You can use nested ForEach commands:
{{DeleteVehicle _x} ForEach (Crew _x)} ForEach ThisList
But I think you might CTD if you try and delete the crew straight out of a vehicle, you might have to SetPos them out first with a slight pause.
{{[_x] Exec "Eject.sqs"} ForEach (Crew _x)} ForEach ThisList
Eject.sqs
_Unit=_This Select 0
_Unit SetPos [0,0,0]
@(_Unit==Vehicle _Unit)
DeleteVehicle _Unit