Phoenix23 mentions that he/she believes the sound 5 to be chuunin but I don't know why that asumption would be made. After all they were beaten indiviually by genins from Konoha. That leads me to belive they were genins as well. As for Kabuto, while I doesn't have the skill level of a genin, neither do a number of genins who have not been promoted. I also doubt that Orochimaru is too concerned rankings, so there is no reason to assume he raised Kabuto's rank. It also seems that the only way to advance is through the exam which Kabuto never completed.