[pdelbarba]

Isn't using a fan to create a low pressure zone not considered a traction device? I doesn't directly contact the ground nor does it actually constitute any solid form of traction as it would rely on a limited power supply. Such a device could not be used continuously throughout the match (just an estimate, no supporting math) as it would deplete the battery and rob power to the wheels. This is, of course, dependent on your drive configuration (four wheel/two wheel drive) and other systems such as pneumatics. This would, however, be very useful for acceleration and cornering if it could be designed with minimal spin-up time.
On a separate note, is there a rule stating that we cannot use any sort if thrust based propulsion system and just mounting the wheels as unpowered casters? Such a device wouldn't even rely on traction at all...