A Sunset boa is just another name for a Super Hypo Hogg. They call them Sunsets because the Hoggy trait tends to bring out more of an orangy color than regular Super Hypo boas.

If you breed two Hypo Hoggs together, you'll get some Super Hypo Hoggs (aka Sunsets).

They aren't really true "hets." The Hypo trait is codominate, so if you breed a hypo to a normal, you get 50% hypos, 50% normals. If you breed a hypo to a hypo, you get 50% supers, 50% hypos.