Are milia a symptom of something more serious?

No: They are extremely common in healthy newborn babies. Milia can occur at any age, especially after blistering of the skin or other types of irritation that can cause the keratin to be trapped in small cysts. Treatment is available if you find them bothersome.

Newborn benign rash: Milia are benign, self-limited lesions that manifest as tiny white bumps on the forehead, nose, upper lip, and cheeks of the newborn. It doesn't have any correlation with serious conditions as to my knowledge.