Of course it is. Attorneys specialize. What does personal injury law have to do with free speech issues ? Or corporate law have to do with sodomite marriage ?
Doctors specialize too, but there isn't a doctor in practice that isn't an expert in human anatomy. Are you saying law students graduate from law school and apply for the bar without studying and knowing the Constitution? What exactly do they study in law school? Isn't the Constitution the very foundation of law in this country? Is it possible to practice law in America without a firm knowledge of the source of that law?