The usage is correct. It also makes clear that the person who is the father figure in John's life currently will participate.
It does not imply living, marital or birth arrangements for you or John's dad. The adult to whom you are referring
- may or may not live with you
- may or may not live with John
- may or may not be married to you
- may or may not be John's biological father
- may or may not have legal guardianship or custody of John
Regardless of which combinations of the options listed above apply, the a male person who has a parental role in John's life will be present. That is probably what the school is most interested in.
That being said, people make all sorts of assumptions about marital status, living arrangements, parental history and so forth, based on their world view, not necessarily based on your communication. That is their problem, not yours.