“Corporeal Cascade” skill node for Death Seal applies the physical type to the Wave(s) of Death visual, but does not change the skill tag, damage type icons (in Skills, the little fist and skull next to its icon), or pre-explosion status visual.
It currently does not receive benefit from +Skill/Spell Physical level-granting items (e.g. Thorn Slinger unique belt, +1 Physical skills) though it does appear to gain benefit from all bonuses to Physical damage (e.g. Valeroot unique chest armor, +10 Spell Physical Damage) to Waves of Death as indicated by the Damage on its tooltip.