I currently have dreads and a nape undercut, am I out of regulation?

Faddish and exaggerated styles, to include shaved portions of the scalp other than the neckline, designs cut in the hair, unsecured ponytails (except during physical training), and unbalanced or lop-sided hairstyles are prohibited. depending on how close your nape undercut is, it may fall under the category of "shaved portion of the scalp other than the neckline". Also there is probably some crusty old CSM out there who would consider it to be "faddish" or "exaggerated". That's the problem with 670-1, it's vague and subjective.