It's true that no one can regenerate from nothing, no matter how powerful they are.
You have to have DNA, the beginning of a living cell, supplemented with the necessary building material to form the specific proteins that make up multicellular organ systems. Because Hulk's DNA&building material needed for proteins grows in strength in proportion to stress, he can always regrow all other organic matter because his DNA is always left intact.
Regeneration is maybe the wrong expression.
But DNA is not necessary for its regeneration.
Hulk can also regenerate when he was transformed into glass or stone.
Even when the Hulk was a spirit that is not stopped his ability to regenerate. Sobalt the spirit has enough (gamma) collected energy he could create a new body.
Even the things which he emerged again with her deception.