There is no specific rule governing the fans, with the exception of the Victor fans, which may be attached directly to the power input terminals on the Victors.
That being said... In past years (which in no way applies to this year), this rule was absent. In its place, we had to connect the Victor muffin fans directly to the power distribution board, although we were allowed to join them all together under one 20A Spike. Teams impressed upon the GDC the safety and ease of connecting those fans directly to the Victor power inputs, and the rules were changed (starting in 2009, i believe... maybe even with a Q&A in 2008).
Using that as a precedence, i would think connecting the fans directly to the power distribution board would be acceptable (protected by a 20A breaker, of course).The fans are very low power devices, designed for moving air through an area with the intent of cooling components. Having them controlled by a spike defeats that purpose, unless the spike is triggered with a temperature sensor placed on the concerned components. Rather, having the fans on whenever the robot is on makes the most sense.
But that is all just my opinion. Please request clarification from the GDC
