What would a child of a Night Hag and an (unfortunate) human(oid) father be?
Changeling, as per the definition 'Child of Hag and Human'? (Problem is, Traits are only given for Annis, Green, and Sea Hag changelings)?
Or Tiefling, as the Night Hag is an evil Outsider native to the Plane of Shadow (making the child being the offspring of an evil Outsider)?
If the Plane of Shadow is involved, I'd assume a Fetchling (Bestiary 2, p123).
Take your pick of whichever seems more appropriate for your character design. Truth is it could just as easily be "none of the above." It could be a normal hag or whatever race the father was and most likely should be a "half (fiendish or hag)" template if you really want to get nit picky. Bloodlines aren't specifically defined, a tiefling could easily come from a "normal" family just because some ancestor generations back had a fling. Think of it as a recessive gene. Choose the race you want, put in an appropriate back story and enjoy.
That being said, the Blood of Fiends is probably the best race book to date and well worth getting if you want some ideas on tieflings.
I bust out the percentile dice.