Is hyperpigmentation a part of hypopituitarism?

No: Not typically as hyperpigmentation if due to adrenal insufficiency, is because there is increased acth hormone signaling. This latter hormone is often missing in individuals with steroid dependent hypopituitarism.

No : Patients with primary adrenal insufficiency become hyper pigmented prior to diagnosis because of really high pituitary production of acth and msh (causes bronzing). Hypopit patients can't make acth, therefore no significant msh. Bronzing is not seen in hypopit patients with secondary adrenal insufficiency.