I'm not sure I understand Jon's post. The original question was that the person was applying to graduate school next year. Doesn't that imply a doctoral program? If so, then how could the question not be taken as "should I go to a program with or without a NP track"?
As some one who is already boarded and who has sat on exec boards, I can tell you that boards do not look favorably on ad hoc education. ABCN has changed standards in 2005 and adopted the HCG as more than aspirational (although not complete). It is no longer acceptable for new students to be unable to substantiate their training in the field by experience alone. If you read the HCG and updates, you will see that there are 4 domains, including general and clinical, are you (Jon/Dr.JT/NPsych) suggesting that those be achieved without academic supprt, I think you are not. However, the postings given are suggesting that the other two domains can be. I can tell you that is becoming increasingly untrue.
You will need to document training in an organized institution. I have seen applicants asked to return to graduate courses in neuroanatomy/neuropathology years after their degree to be eligible to sit for boards.
As to the mentor, I am not saying it is not a good idea, but I think Jon is mischaracterizing this point and it may be because he interpreted the post as a request for undergraduate programs.
You are wellcome to take all these posts and do the research yourself, but I urge you to carefully consider what I am saying. The pulse of the field is changing and the politics with it. The advise given to others when they went through is not going to be the same as for you. I am very wary of students without formal training and APPCN fellowships are no longer approved without an ABCN (although they may start allowing ABPN/ABPdN soon) as the director.