A protection oath is basically a citizenship paper declaring that sailors birthplace with signatures of proof from like a parent or close friend declaring the info to be true. The purpose was to keep the British or any other navy from impressing that person into their navy, especially during the war of 1812. They are found in the Custom House records of seaports.
As far as the white Bent genealogy yes they were some slave holders but do not depend on the info from it.
Isaac was born in Burdickville R.I. in May 1827 from his obit and nothing I ever found linked him to Prince. Not to say there wasn't a connection either.