There are several discussions on damage, or not, from rolling tractors. The odds are of everything being ok, but there is also the possibility of oil leaking past rings and into upper cylinders. THAT is not good and it only takes a little time to remove that as a possibility. Read the following link for suggestions made in a similar situation.
http://www.tractorbynet.com/forums/kubota-owning-operating/159819-rolled-my-tractor-engine-wont.html
Hope all is ok, but most agree you should not try to start it until you have verified you have no oil in the cylinders. Trying to compress oil could be an expensive "turn for the worse."