This is a policy decision each PTO needs to make. There's no one "right" answer. I belong to two PTO's. One has it in it's bylaws that no school employee or district employee at a managerial level can be an officer.
The other has no such clause and the school nurse was the President a couple years ago and teachers have also been officers. (Note - these people were all parents of children in the school, as well as being employees.)
It is written in our bylaws that a parent can be an exec member only if they are acting as a parent not as an employee of the school. Needless to say, this has caused conflict in the past.
The irony of commitment is that it’s deeply liberating-in work, in play, in love. The act frees you from the tyranny of your internal critic, from the fear that likes to dress itself up and parade around as rational hesitation. To commit is to remove your head as the barrier to your life. --Anne Morris