It's not unheard of to have the secretary office combined with the treasurer and it is looked at as one vote but if you want the answer NO one person per office I'm not finding it in my Robert's Rules of Order 9th Edition.
I wrote to a Q & A on Robert's Rules of Order site to see if there was anything that stated that one board member could not hold more than one board position. I wonder if anyone knows what the rule is? Each person on the board has the right to a vote and if someone holds more than one board position than that person only can have one vote. There is still the question of whether it is allowed according to Robert's Rules which most organizations use to run their by laws.