not controllable in in reveng.xml (yet), but a custom strategy can do it:
Code:
public class YourRevEngStrategy extends DelegatingReverseEngineeringStrategy {
public YoirRevEngStrategy(ReverseEngineeringStratregy re) {
  super(re);
}
   public String getOptimisticLockColumnName(TableIdentifier identifier) {
                  if("theTable".equals(identifier.getName())) {
                       return "DMUTDAT";
                  } else {
         return super.getOptimisticLockColumnName(identifier);
                 }
   }
}
you can also choose to implement useColumnForOptimisticLock instead, but that is up to how you like to decide what the column is.
note that to have it be a timestamp the type of column should be something that is compatible with a timpestamp (date,timestamp,etc)