I've never read poetry from Melville so I can't say anything about the quality of this poems or what Melville thought about them himself.
But if Melville thought they are an importaint part of his work they should be included, I think.
This is always a difficult decision.
Nietzsche's Kritische Gesamtausgabe doesn't contain his scientific work he wrote as a young adult, since it has nothing to do with his philosophical works he wrote later. But it contains his private notes and his letters since this material helps to understand Nietzsche's thinking with more depths. Within Nietzsche scholarship this exlusion of Nietzsche's very early works is normal.
To make things easier I'll offer a large amount of money, karma and sailors to the bookmaker.