No, though in some states that wouldn't hold up anyway, given that he readily admits that they had the sort of relationship from which they could "break up". He was stupid to do it, and she was stupid to use somebody stupid as a donor. Heck, it only costs about $300 to use a reputable bank, and get a sharp PhD or MD or JD who's been screened for a raft of diseases and genetic problems. This poor kid will probably have an IQ of about 60, given the parents' mental abilities.
Child support is the right of the child, not the mother. There is nothing that the mother can sign that ends the right of the child to be supported by the father.
And yes, the mother is the guardian of the child, so if she changes her mind and decides to exercise the option of seeking support for the child it is as legal as church on Sunday.
Every man should be made aware of this.