Anthony D'Amato at Northwestern argues against such appointments in a new article here. As he notes on page 68 of the article, his own Dean, David Van Zandt, has taken the opposite view denying "that law is an autonomous discipline having its own methods and approach. [Dean Van Zandt] claims instead that 'law and legal institutions are merely a subset of social and political phenomena that are studied every day in economic, political science, and other departments.'"
This should make for some lively faculty meetings!
I haven't read all of Professor D'Amato's article, though, needless to say, I'm skeptical about the strong conclusions it draws--though perhaps the Northwestern experience colors his perspective in particular.
UPDATE: Josh Wright (George Mason) has useful things to say in response to Professor D'Amato's claims about law and economics.
ANOTHER: More critical reaction from Dan Markel (Florida State).
AND ONE MORE: The legal historian Mary Dudziak (USC) is also skeptical.