[Wayne Doenges]

Here is the whole rule:

<R27> Robot wheels, tracks, and other parts intended to provide traction on the playing field (“traction devices”) may be purchased or fabricated. In no case will traction devices that damage the carpet or other playing surfaces be permitted. Traction devices may not have surface features such as metal, sandpaper, or hard plastic studs, cleats, or other attachments. Anchors, i.e. devices that are deployed/used to keep one’s robot in one place and prevent if from being moved by another robot, cannot use metal in contact with the carpet or other playing surfaces to “stay put.” Gaining traction by using adhesives or Velcro-like fastener material is not allowed.

It specifically mentions "Traction Devices". My opinion is that if you are using metal casters to support your robot, not driving, it should be OK. YMMV

Wayne Doenges
CAD Mentor