Please read MILPERSMAN 1440-010 and 1440-020. MILPERSMAN 1440-010 lists the primary reasons for forced conversions, medical is one of them, medical documentation is required with the "Forced conversion" package. MILPERSMAN 1440-020 states "Forced Conversion" will not normally be approved for NC, but waivers are considered on Case-by-Case basis. So there are no black and white on this. As long the member meets all the other requrements it shouldn't be a problem. You will have to work closely with your Career Counselor ISIC on this.
FYI.. I know a couple NCs that converted due to medical reasons, so it has been done before.