i think its for keeping the ass end straight since theyve obviously lost down force with the smaller rear wings. basically its acting as a rudder, keeping the vehicle straight. all the air going by will keep the ass end in line, making the car less twitchy.
edit: and helps direct air where they want it, the wing.
As erik said, aerodynamics have as much to do with the management of air over/through/around/under the car, as it does for the car being able to cut through it. The aim of these fins is to improve the quality of the airflow directed towards the rear wing, increasing its efficiency in terms of increased downforce and reduced drag.
The VR01 looks very nice. Probably one of the more graphically appealing cars in recent years. I can't help not to think of a GP2 car when I do see this one
The Virgin's nose (from that angle at least) looks pretty pointy, almost like an IRL car. I know its not as low and the wing isnt the same, but to me it looks like that.
EDIT: maybe not Unsecure image, only https images allowed: http://cdn.virginracing.com/1265215186/galleries/car/01_VR-01_Front.jpg