It shouldn't. You'd need to check the PTO bylaws, but those would be some extremely rigid ones to define membership that narrowly. Usually, PTO member (and thus ability to be an officer) is one of the following:

* any parent/guardian of a student at the school or any staff member of the school
* anyone in the local community
* anyone interested

Usually it's a question of if membership is wide open (anyone who feels like it can join) or restricted more to the specific stakeholders of the school.

Under our own definitions, you are a "parent". We don't distinguish between custodial or non-custodial. It's hard to imagine making that distinction as long as the person still has some parental rights regarding the child.